6th to 8th Grade - Gateway 2

The instructional materials reviewed for Grades 6-8 meet expectations that they present disciplinary core ideas (DCIs), science and engineering practices (SEPs), and crosscutting concepts (CCCs) in a way that is scientifically accurate. Across the grades, the teacher materials, student materials, and assessments accurately represent the three dimensions and are free from scientific inaccuracies.

The instructional materials reviewed for Grades 6-8 meet expectations that they do not inappropriately include scientific content and ideas outside of the grade-band disciplinary core ideas (DCIs). Materials contain no instances where non-scientific content or ideas are included as science ideas, no instances where scientific content or ideas are included without meaningful connections to grade-band DCIs, and no instances where DCIs from above or below the grade band are included without meaningful connections made to the grade-band DCIs.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate all grade-band disciplinary core ideas for physical science. Across the series, materials incorporate all grade-band components and all the associated elements of the physical science DCIs; one element is partially addressed. For a given DCI, all elements are typically included within the same unit and approached with a variety of activities. Most of the physical science DCIs are incorporated within the five physical science units: three are found in Grade 6, one in Grade 7, and one in Grade 8; one physical science DCI is addressed in a Grade 7 life science unit on life’s chemical processes.  

Examples of grade-band physical science DCI elements present in the materials:

• PS1.A-M2. In Grade 7, Unit 6: Lesson 2: Exploring the Burning of Hydrogen, students observe the flammability of gases via video and document the characteristic properties of hydrogen, helium, and air. In another activity, they observe tealights and glass jars to find what happens to the flame when the tealights are covered in order to learn what causes a substance to burn. During the lesson’s last activity, students use the properties of common gases to determine what kind of gas is found in different test tubes by using evidence from the investigation and information on the properties of common gases. Students also apply their learning about the characteristic properties of hydrogen to explain the cause of the Hindenburg explosion and propose what may have stopped it from burning.

• PS1.A-M3. In Grade 6, Unit 3, Lesson 2, Activity 2: Where Does the Water Come From?, students record observations, list questions, and gather information through reading, discussing, and looking at pictures. Students then construct an explanation for the formation of water droplets on the outside of a glass of ice water by temperature differences to the different states of matter and the movement of molecules within each state.

• PS1.A-M4. In Grade 6, Unit 3, Lesson 4, Activity 9: Icy Conditions, students construct an explanation for how ice forms on air conditioner coils that uses the concepts of molecular movement, states of matter, and energy flow. They describe how the "warm air blowing over the coils transfers heat to the cold coils. As a result, the water molecules in the air lose energy and slow down to form water droplets on the coils.” The liquid water would then transfer energy to a colder surface or substance in order for the ice to form.

• PS1.A-M5. In Grade 7, Unit 6, Lesson 4, Activity 12: Starting a Reaction, students conduct an investigation about steel wool and rust and answer questions to explain the different structures of the molecules in gases and solids. Students are given a diagram of subunits of iron oxide (three oxygen atoms and two iron atoms) and then given a larger version of the diagram from which they select eight subunits. 

• PS1.A-M6. In Grade 6, Unit 3, Lesson 4, Activity 11: How Temperature, Pressure, and Volume are Related, students watch the teacher demonstrate covering a bottle with a balloon and placing it in a tub of hot water causing the balloon to inflate, then moving the bottle into a tub of cold water and watching the balloon deflate. Students record their observations and discuss their answers. Then, students create a model of the inside of the bottle before heating, after heating, and after cooling to show the relationships between temperature, pressure, and volume, including the movement of molecules.

• PS1.B-M1. In Grade 7, Unit 6, Lesson 2, Activity 6: Hands-On Investigation: Electrolysis, students analyze the gases found in the two test tubes following the running of electrolysis, a chemical reaction. By applying an understanding that new substances are created from a chemical reaction, they use the characteristics of gases to determine what new substances are in each test tube.

• PS1.B-M2. In Grade 7, Unit 6, Lesson 3, Activity 8: Candy Chemical Reactions, students use models to explain what happens to molecules in different chemical reactions. For example, along with the image of a burning candle, the materials present two representations of the chemical reaction: paraffin wax + oxygen → carbon dioxide + water and 2C16H34 +49O2 → 32CO2 + 34H2O. Students then list the number of molecules before and after the reaction for paraffin, oxygen, carbon dioxide, and water and list the number of atoms for carbon, hydrogen and oxygen.

• PS1.B-M3. In Grade 7, Unit 6, Lesson 4, Activity 12: Starting a Reaction, students conduct an investigation about steel wool and rust, and then predict and explain, "Does metal rusting require energy, or does it release energy like the Hindenburg explosion?" They are also given a set of procedures and asked to rewrite them to include steps for collecting data on energy changes. At the end of the activity, students summarize what they figured out about energy and matter.

• PS2.A-M1. In Grade 6, Unit 1, Lesson 4, Activity 10: Two Colliding Cars, students explain how a collision seen in a video demonstrates Newton’s third law of motion and create a model of what happens in the video: they demonstrate that the pair of interacting objects exert forces of equal strength on each other but in the opposite direction. 

• PS2.A-M2. In Grade 6, Unit 1, Lesson 2, Activity 5: Hands-On Investigation: Interacting Forces, students investigate a spring-loaded cart, identify the component of the system and interaction of forces, and demonstrate that the motion of the cart is determined by the sum of the forces acting on the cart.

• PS2.A-M2. In Grade 6, Unit 1, Lesson 2, Activity 7: Hands-On Activity: Designing a Balloon-Powered Car, students test the effect of mass on the balloon-powered car and write a concluding statement that explains the greater the mass of the object, the greater the force needed to achieve the same change in motion. 

• PS2.A-M3. In Grade 6, Unit 1, Lesson 3, Activity 3: Fire Extinguisher Go-Kart, students make a model of the fire extinguisher go-kart system to establish a frame of reference and demonstrate the position and direction of forces and motions being described within that frame of reference.

• PS2.B-M1. In Grade 6, Unit 2, Lesson 3, Activity 9: Hands-On Investigation: Push and Pull, students conduct an investigation with magnets and iron filings to gather data on magnetic fields and determine the strength and direction of magnetic forces.  

• PS2.B-M1. In Grade 6, Unit 2, Lesson 4, Activity 17: Hands-On Investigation: Sticky-Tape Lab, students plan and conduct an investigation into electrical forces using tape and compare their findings with that of magnetic forces.

• PS2.B-M2. In Grade 6, Unit 2, Lesson 2, Activity 5: Gravity at Different Scales, students explore gravitational force and the role of scale on its strength. After investigating dropped objects and the role of air on the falling objects, students read historical accounts of the “discovery” of gravity for very large and very small objects. Students are then asked to "describe the scale at which gravity is acting on the levitating-orb system” and to “compare the gravitational forces exerted by Earth, the orb, and the pipe."

• PS2.B-M3. In Grade 6, Unit 2, Lesson 2, Activity 6: Hands-On Investigation: Gravity, Force, and Mass, students simulate earth’s gravitational force by investigating the relationship between force (measured with a spring scale) and mass to determine if gravity exerts an equal amount of force on all objects. Using the results, they predict what would happen if the same experiment was conducted on the moon and consider what would be the relationship between the force and objects with different masses.

• PS2.B-M3. In Grade 6, Unit 2, Lesson 3, Activity 9: Hands-On Investigation: Push and Pull, students conduct an investigation with magnets and iron filings to gather data on magnetic fields and determine the strength and direction of magnetic forces.

• PS2.B-M3. In Grade 6, Unit 2, Lesson 4, Activity 16: What Causes Charge?, students investigate electrical fields by observing and recording the behavior of charged balloons.  

• PS3.A-M1. In Grade 6, Unit 1, Lesson 4, Activity 10: Two Colliding Cars, students read data and create graphs in order to explain which factors have the greatest effect on kinetic energy and demonstrate that motion energy is proportional to the mass of the moving object and grows with the square of its speed.

• PS3.A-M2. In Grade 6, Unit 2, Lesson 5, Activity 21: Energy Transfer, students observe two systems, a junkyard magnet, and a stretched rubber band, and compare the potential energy in each.

• PS3.A-M3. In Grade 6, Unit 3, Lesson 2, Activity 2: Where Does the Water Come From?, students observe water forming on the outside of a glass of ice water and then gather information about the difference between heat and thermal energy. Through reading text and discussions, they determine how thermal energy and its relation to molecular movement can help explain how water droplets formed on the outside of the cup. 

• PS3.A-M4. In Grade 6, Unit 3, Lesson 5, Activity 18: Heating Curve Segments, students analyze a heating curve to determine where the changes of state are occurring. After a discussion, they show how matter and energy are related in each curve segment and describe the decrease of potential and kinetic energy in relation to the states of matter. 

• PS3.B-M1. In Grade 6, Unit 1, Lesson 1, Activity 2: Before and After Videos, students create a model of a rocket sled collision showing the parts of the system before, during, and after the collision in order to demonstrate that when the motion energy of an object changes, there is change in energy at the same time.

• PS3.B-M2. In Grade 6, Unit 3, Lesson 4, Activity 12: How an AC Cools Part 2, students evaluate different subsystems of the air conditioner system by noting within each system the transfer and direction of energy flow; what happens to the pressure, temperature, thermal energy, and state of matter of the various substances involved; and what happens to the molecules that make up the substances in terms of motion, state, kinetic energy, and potential energy. Keeping in mind the energy transfer, temperature, and substances involved, students share and discuss their theories about how the problem of ice formation on the air conditioner is likely happening.

• PS3.B-M3. In Grade 6, Unit 3, Lesson 6, Activity 20: Unit Project: Unwanted Frost on the Window, students are presented with the problem of ice forming on the interior side of windows. Applying knowledge of heat transfer and changes of state, students form ideas for why the ice is forming and, with pairs or in small groups, explain possible solutions. In their explanations and proposals, students specifically identify how heat transfers out of hotter regions or objects into colder one, in order to provide a possible solution to keep ice from forming on the air conditioner.

• PS3.C-M1. In Grade 6, Unit 2, Lesson 6, Activity 23: Levitating-Orb Reboot, students apply the relationship between force and energy transfer to the phenomenon of the levitating orb and identify the subsystems which interact with one another that result in the levitating orb. They then construct an explanation to include the cause and effect relationship between the type of force applied and the kind of energy that is transferred.

• PS3.D-M1. In Grade 7, Unit 7, Lesson 2, Activity 8: Hands-on Investigation: Making Food, students read about photosynthesis and refine a previously created model of two kelp forests to include the process of photosynthesis and thereby demonstrate the chemical reaction where plants produce sugars from sunlight and release oxygen.

• PS3.D-M2. In Grade 7, Unit 7, Lesson 3, Activity 10: Potato Time-Lapse, students explain that a sprouting potato decreases in size as the sprouts from the potato increase due to the molecules of starch rearranging back to sugar so the plant can grow. Their explanation demonstrates that chemical reactions in plants release stored energy used for plant growth. Student explanations do not discuss this reaction in relation to oxygen and the production of carbon dioxide and other materials.

• PS3.D-M2. In Grade 7, Unit 7, Lesson 3, Activity 12: Releasing Energy, students read about cellular respiration then describe how energy is released by living things and add this understanding to clarify cellular respiration.

• PS4.A-M1. In Grade 8, Unit 11, Lesson 3: Modeling Sounds, students begin with correlating the vibrations caused by sound with the wave motion of a spring. In the next activity, they quantify the wave movement of a spring toy and describe two ways they can change the motion of the spring and what parts of the wave changes when the spring is moved a farther distance up and down. In a subsequent activity, they complete sentence starters describing the wave if the music is louder and faster and has lower pitch.

• PS4.A-M2. In Grade 8, Unit 11, Lesson 4, Activity 13: How Sound Travels, students observe a video of a tuning fork in water and discuss how sound is transmitted through both water and air. Citing their evidence gathered on energy transfer via particle movement, they then construct an explanation of how sound waves are transferred through matter.

• PS4.B-M1. In Grade 8, Unit 11, Lesson 5, Activity 18: Hands-on Investigation: The Properties of Light, students conduct an investigation with a light, prism, and colored filters. Students are asked to explain what happens to different colors of light when a white beam of light shines on red paper, what evidence supports that it is possible for a material to let some colors of light through but not others, and propose an explanation for how lights of different colors differ.

• PS4.B-M2. In Grade 8, Unit 11, Lesson 5, Activity 17: Interactions of Light and Matter, students conduct an investigation about the behavior of light waves and gather data on how it interacts with other materials. They complete a graphic organizer where they provide examples from the lab to match vocabulary terms of light behavior (propagation, reflection, etc.). Students are asked to review their data table and evaluate similarities and differences in how light behaves when it interacts with the various test materials and identify patterns in the behavior of the light.

• PS4.B-M3. In Grade 8, Unit 11, Lesson 5: Wireless Signal, Activities 17-18, students investigate how light interacts with different materials. Students record observations and use their data to determine whether each material reflects, refracts, or absorbs light. Students answer questions about different behaviors of light, providing examples from their investigation. Students use color filters to observe that white light is a mixture of different colors and analyze how a prism breaks up white light as a result of different frequencies (colors) being bent varying amounts by the prism. Students conclude that the color of light seen depends on the frequency of the light wave,  and that the brightness of the light depends on the amplitude of the light wave.

• PS4.B-M4. In Grade 8, Unit 11, Lesson 5, Activity 15: Cell Phone in a Vacuum, students watch a video of a cell phone in a vacuum showing that the phone does not make any sound but the display lights up. They make a claim and use evidence to explain if the wireless signal between the cell phones travels through a vacuum. The materials also include the following prompts: "Can the wireless signal between the cell phones travel through a vacuum?" and "Is it possible that the wireless signal between the cell phones travels as sound waves?” Through answering, students determine that light travels through space but cannot be a matter wave. 

• PS4.C-M1. In Grade 8, Unit 11, Lesson 6, Activity 20: Signals in the System, students use models to simulate the transmission of analog signals and explain how they become distorted during transmission and that digital signals are more reliable. To simulate passing analog signals, one student copies a wave of music on a blank sheet of paper. This drawing is passed to a second student who draws a copy of the first student's drawing, this is repeated with a third student copying the drawing of the second student. The students then compare the final drawing to the original. To simulate converting an analog signal to digital, graph paper is used. A comparison is made with these drawings.

Example of a grade-band physical science DCI element that is partially present in the materials:

• PS1.A-M1. In Grade 7, Unit 6, Lesson 3, Activity 7: Modeling Molecules, students create models of different molecules, analyze their models, and draw conclusions about how atoms combine in different ways and amounts to form different molecules or substances. The activity does not address the understanding that molecules range in size from two to thousands of atoms.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate all grade-band disciplinary core ideas (DCIs) for earth and space sciences. Across the series, materials incorporate all grade-band components and the associated elements of the earth and space science DCIs; however, two elements (ESS3.A-M1 and ESS3.C-M1) are partially addressed. For a given DCI, all elements are typically included within the same unit and approached with a variety of activities. All earth and space science DCIs are incorporated within the five earth and space science units: one unit is found in Grade 6, two in Grade 7, and two in Grade 8. 

Examples of grade-band earth and space science DCI elements present in the materials:

• ESS1.A-M1. In Grade 6, Unit 4, Lesson 3, Activity 5: Patterns in Shadows of the Red Moon, students revisit their physical model of the sun-earth-moon system from the previous activity to replicate the observable shadows as shown in the lunar eclipse video. They plan and use their model to collect data. Lastly, they draw a revised model using new information to explain the shadow patterns observed. 

• ESS1.A-M2. In Grade 6, Unit 4, Lesson 5, Activity 15: Closer Look at Planetary Objects, students view an image of Jupiter and compare it to previous observations. They conduct additional research about a planetary object including images and data obtained from technology tools. They record properties of the object researched and cite sources of evidence. After sharing their research, they read about the Milky Way galaxy being one galaxy in the estimated two trillion galaxies in the observable universe and watch a video on how the Hubble Telescope works to uncover other galaxies. Lastly, they explain how their models help explain the shape of the Milky Way.

• ESS1.B-M1. In Grade 6, Unit 4, Lesson 5, Objects in the Night Sky, students observe a teacher demonstration that models motion in space with different sized marbles moving around a circular stretched fabric background. They also watch two videos, "Gravity and Speed" and "Gravity and Orbits" to broaden their learning. In the next lessons, students discuss their knowledge of the planets, planet properties, and how planets move in space. They apply their understanding of orbits from the previous activity to the following prompt: "Your Earth-sun-moon models in this unit have represented Earth orbiting around the sun as evidence for the patterns in moon phases and lunar and solar eclipse observations. The mass of the sun is 333,000 times more than the mass of Earth. Based on your models and the additional planetary data, can you support the claim that the other planets are also orbiting around the sun?"

• ESS1.B-M2. In Grade 6, Unit 4, Lesson 4, Activity 7:The Disappearing Sun, students watch videos of both solar and lunar eclipses and then explain the causes of both and how they are similar and different. They include ideas about the causes of the shadows, the moon phases, the position and motions within the earth-moon-sun system, differences in colors, and how light from the sun interacts with the system.

• ESS1.B-M2. In Grade 7, Unit 10, Lesson 4, Activity 10: Modeling the Seasons in Alaska, students observe a teacher demonstration of the sun-earth model and the revolution of earth around the sun and collect data of how the intensity of light changes on the location on the globe. Students then fill in the blanks of a paragraph describing seasons and solar radiation.

• ESS1.B-M3. In Grade 6, Unit 4, Lesson 5, Activity 14: Other Objects in Space, students observe an image of the Milky Way galaxy and record their observations. They watch a video describing the formation of the solar system from the beginning of the solar nebula through the discussion of two possible theories as to what triggers the materials to clump together. They read a passage that describes the role of gravity in the formation of planets and then compare the formation of earth's moon to the formation of the solar system. After writing what questions they have, they reflect on the demonstration of the force of gravity on objects in space and use evidence from the video and passage to explain how the model represents the formation of planetary objects.

• ESS1.C-M1. In Grade 8, Unit 15, Lesson 2, Activity 7: Rock and Roll, students label layers of rock in order of relative age demonstrating that a geologic time scale interpreted from rock strata provides a way to organize earth’s history by relative age only.

• ESS1.C-M1. In Grade 8, Unit 13, Lesson 2, Activity 2: Colossal Fossil Jostle, students complete an interactive simulation that explores the chronological order of fossils in conjunction with the relative ages of rock layers. They construct an explanation about how the fossil record reveals earth’s history and how rock layers and organisms change over time.

• ESS1.C-M2. In Grade 8, Unit 15, Lesson 3, Activity 10: Ocean Ridges, students explain the type of boundary interaction responsible for the formation of ocean ridges, demonstrating that tectonic processes continually generate new ocean seafloor at the ridges.

• ESS2.A-M1. In Grade 8, Unit 15, Lesson 2, Activity 5: Hands-On Investigation: Plate Interactions, students use previous experience with energy transfer from convection and information about plate boundary interactions to explain the processes that occur at each type of boundary. The explanation demonstrates that earth’s processes are a result of energy flowing from matter cycling due to energy within earth’s hot interior producing physical changes in earth’s crust.

• ESS2.A-M1. In Grade 7, Unit 9, Lesson 2, Activity 3: Cloud Energy, students explore the role of energy from heat, specifically the sun, and gravity in the movement of water within a system. After observing a teacher demonstration, students analyze data patterns between the amount of snow and temperatures in order to build their understanding of cloud formation. Applying this understanding of clouds, they describe how changes in energy drive water movement within storms, and add to their model to show the various impacts of the sun’s energy on the storm system.

• ESS2.A-M1. In Grade 7, Unit 7, Lesson 3, Activity 12: Releasing Energy, students explore the transfer of energy through the processes of photosynthesis and cellular respiration. After reading how energy, beginning with that from the sun, flows through these processes and analyzing the accompanying models, students construct an explanation to describe the flow of energy and the movement of matter within an organism.

• ESS2.A-M1. In Grade 8, Unit 15, Lesson 3, Activity 9: Down in the Trenches, students read about the Puerto Rico Trench and Sonar Mapping. After discussing how Sonar Mapping could lead to scientists' creation of ocean floor mapping, students analyze images of ocean trenches and plate tectonics. They create a model of the "interaction of the Caribbean and North Atlantic Plates at the Puerto Rico Trench." This learning continues into Activity 10: Ocean Ridges when students explain the type of boundary interaction responsible for the formation of ocean ridges, demonstrating that tectonic processes continually generate new ocean seafloor at the ridges.

• ESS2.A-M2. In Grade 8, Unit 15, Lesson 4, Activity 12: Energy Data, students describe potential causes for stone arch formations including a timescale for formation to happen and explain how patterns of earthquakes at different scales of time and space relate to energy. This demonstrates the planet’s systems interacting over scales of time and how these interactions have shaped earth’s history and will determine its future.

• ESS2.A-M2. In Grade 8, Unit 15, Lesson 4, Activity 14: Puerto Rico Rocks, students explore the microscopic process of change in mechanical weathering to explain what caused the arch to form and the amount of time this process would take.

• ESS2.B-M1. In Grade 8, Unit 15, Lesson 2, Activity 3: Continent Puzzle, students support the claim that continents were originally one large landmass selecting evidence provided in a video model of continental drift. Maps showing the apparent fit of present day continents lead to a discussion of Pangea and make clear how earth's plates have moved great distances, collided, and spread apart to result in the current location of continents.

• ESS2.C-M1. In Grade 7, Unit 9, Lesson 2: Rainstorms and Snowstorms, students explore the cycling of water through the spheres via evaporation, condensation, and precipitation. In Activity 2, students study cloud formation via demonstration and investigation. In Activity 4, they explore cycling of water through the spheres via crystallization. Through video and data sets, they also explore the relationship between temperature and precipitation types.

• ESS2.C-M1. In Grade 7, Unit 9, Lesson 3, Activity 6: The Water Cycle, students explore the cycling of water through the spheres and the role of downhill flows on land within that cycling. Students read an article about groundwater and how it comes to be and then develop a model of the water cycle showing the roles of evaporation, condensation, precipitation, and downhill flow on that cycling.

• ESS2.C-M1. In Grade 7, Unit 9, Lesson 4, Activity 7: Hands-On Investigation: Water and Plants, students explore the cycling of water through the spheres via transpiration and investigate the role of vegetation density and temperature change on precipitation amounts.

• ESS2.C-M2. In Grade 7, Unit 9, Lesson 6, Activity 12: Predicting the Superstorm, students explore the use of probability for weather forecasting. They read a passage describing how meteorologists used models to predict the superstorm and describe a time when forecasting was different than what was experienced. Lastly, students develop a weather prediction for a given location where they use various maps to analyze how the location, (i.e, landforms, distance to oceans) along with the patterns of wind movements impact weather.

• ESS2.C-M3. In Grade 7, Unit 9, Lesson 2, Activity 3: Cloud, students explore the role of energy from heat, specifically the sun, and gravity in the movement of water within the system. After observing a teacher demonstration, students analyze data patterns between the amount of snow and temperatures in order to build their understanding of cloud formation. Applying this understanding of clouds, they describe how changes in energy drive water movement within storms, and add to their model to show the various impacts of the sun’s energy on the storm system.

• ESS2.C-M4. In Grade 7, Unit 9, Lesson 5, Activity 12: Observing Ocean Currents, students watch a video that shows the different temperatures in water creating convection currents. After watching the demonstration, students draw what they saw and explain why they think it happened. This activity specifically focuses on temperature differences driving currents.

• ESS2.C-M4. In Grade 7, Unit 9, Lesson 5, Activity 13: Modeling Ocean Currents, students conduct an investigation to explore salinity and ocean currents. Using this knowledge, along with the previous activity which explores temperature and ocean currents, students use their models to answer questions about impacts of the ocean, specifically in relation to Alaska. Students then review diagrams of the ocean conveyor belt and summarize their understandings of ocean currents.

• ESS2.C-M5. In Grade 8, Unit 15, Lesson 4, Activity 16: Agents of Change, students describe factors that helped shape natural arches on the coastline of Puerto Rico, demonstrating that water’s movements cause weathering and erosion and change the land’s surface features. 

• ESS2.C-M5. In Grade 8, Unit 15, Lesson 4, Activity 15: Cave Formation, students discuss how they think the arches were formed and examine images of caves in Puerto Rico. Taking what they know about formations on the surface of earth, they investigate and explain how caves could have formed underground. After completing an investigation to show how saltwater forms on strings connecting two beakers of water, students examine structures found in caves and talk about how rainwater can impact the formations underground.

• ESS2.D-M1. In Grade 7, Unit 10, Lesson 4, Activity 11: Hands-On Investigation: Changing Temperatures and Distance from the Sea, students complete an investigation  modeling how sunlight changes the temperature of different substances. In conclusion, students are given the scenario of three different cities - one surrounded by dark-colored, rocky surfaces, another by light-colored surfaces, and a third on the edge of a lake. Students select and justify which city would likely have the highest summer air temperature and why. They also select and justify which would have the warmest average winter temperature and why.

• ESS2.D-M2. In Grade 7, Unit 9, Lesson 6, Activity 12: Predicting the Superstorm, students explore the use of probability for weather forecasting. They read a passage describing how meteorologists used models to predict the Superstorm and describe a time when the forecast was different from what they experienced. Then, students develop a prediction for a given location.

• ESS2.D-M3. In Grade 7, Unit 9, Lesson 5, Activity 13: Modeling Ocean Currents, students conduct an investigation to explore salinity and ocean currents. Using this knowledge with the previous activity which explores temperature and ocean currents, they use their models to answer questions about impacts of the ocean, specifically in relation to Alaska. Students then review diagrams of the ocean conveyor belt and summarize their understandings of ocean currents.

• ESS3.B-M1. In Grade 7, Unit 9, Lesson 6, Activity 14: Getting Ready for the Storm, students explore the history of natural hazards in order to predict future events. Students analyze maps of natural weather hazards and why people would want to know this information.

• ESS3.B-M1. In Grade 8, Unit 15, Lesson 5, Activity 17: Natural Hazard Detection Systems, students select and justify a location for an earthquake-detection monitoring station based on evidence from a map, demonstrating that map information and understanding geologic forces can help forecast locations and future events.

• ESS3.C-M2. In Grade 8, Unit 16, Lesson 4, Activity 11: Farming and Population Growth, students analyze data on human population, crop size, and fertilizer to identify patterns. They use their information to explain the occurrence of the first documented dead zone in the Gulf of Mexico. Student learning is applied during the final project when they complete a design project to construct a solution that prevents the dead zone.

• ESS3.D-M1. In Grade 7, Unit 10, Lesson 7, Activity 17: Human Activity and Effects on Climate Change, students analyze two graphs: Trends in Atmospheric Carbon Dioxide (specifically noting the role of fossil fuels) and Global Yearly surface temperatures. They then construct an explanation as to how fossil fuels affect the atmosphere and temperatures. Using scientific and technical information from the graphs and reading passage, students construct an explanation about the role of humans in this relationship and update their model to show how this information could impact the Alaska dogsled race route.

Examples of grade-band earth and space science DCI elements partially present in the materials:

• ESS3.A-M1. In Grade 8, Unit 16, Lesson 5, Activity 13: Mississippi Barges, students obtain and communicate information on the watershed of the Mississippi, uneven distribution of resources upon which humans depend, and how they are transported by barges on the Mississippi River. They create an infographic to communicate what they learn about resource distribution and transportation of nonrenewable and renewable resources. They analyze and draw conclusions about the transport of resources along the Mississippi, the flow of water in and out of the watershed, and how these connect agriculture, mining, and fertilizer across the transport system. Whereas students read that sand and gravel were unevenly deposited 10,000 years ago by glaciers and that coal comes from ancient swamps over hundreds of millions of years old that only occurred in certain places, the materials do not specifically address the concept that past geologic processes caused the uneven distribution of these resources.

• ESS3.C-M1. In Grade 8, Unit 16, Lesson 3, Activity 8: Nutrients and the Watershed, students read a passage about nutrients found in the Mississippi River watershed and analyze a map of the total nitrogen entering the system, a pie chart of sources of the nitrogen, and a map of atmospheric nitrogen. Then they develop a model of the Mississippi River Watershed system and use this learning to refine models of the dead fish in the Delta. Through refining their models, they deepen the explanation for how humans can impact the environment: in this case, the influx of nitrogen can cause dead zones in certain habitats. The materials do not address how changing the environment can have positive impacts for different living things.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate all grade-band disciplinary core ideas (DCIs) for engineering, technology, and applications of science. Across the series, materials incorporate all grade-band components and associated elements of the engineering, technology, and applications of science (ETS) DCIs. All lessons with ETS elements fall at the end of the unit and serve as the culminating unit project. These may include multiple elements of the same DCI or more than one element across different ETS DCIs or components. 

The materials include ETS DCIs in four physical science units, one life science unit, and one earth and space science unit. Across the series, ETS DCIs are incorporated within three Grade 6 units, two Grade 7 units, and one Grade 8 unit.

Examples of grade-band engineering, technology, and applications of science (ETS) DCIs present in the materials:

• ETS1.A-M1. In Grade 6, Unit 3, Lesson 6, Activity 20: Unit Project: Unwanted Frost on the Window, students are presented with the problem of ice forming on the interior side of windows. They read about how engineers design solutions and specifically note criteria and constraints. After discussing as a class and reviewing their knowledge on heat transfer and changes of state, students create a list of criteria and constraints for solutions to the icy window problem. They brainstorm ideas for why the ice is forming and, with pairs or in small groups, brainstorm possible solutions to keep this from happening. Using various criteria and a Pugh matrix, students rate the possible solutions and construct an explanation for which solution they would propose based on their evaluations.

• ETS1.B-M1. In Grade 6, Unit 1, Lesson 5, Activity 12: Unit Project: Hands-On Engineering: Defining Design Problem, students use a balloon powered car developed in a previous lesson to perform in competition events. They determine the changes that need to be made to the car, applying scientific principles based on the event, and test designs before being implemented. They conduct several tests after each modification in order to determine the effectiveness of the changes before each event.

• ETS1.B-M2. In Grade 7, Unit 10, Lesson 6, Activity 29: Unit Project: Researching a Local Habitat, students explore a process for evaluating a solution to a problem by how well it meets given criteria and constraints. They read through a provided multi-species plan to identify how each feature is important to the success of the plan. 

• ETS1.B-M3. In Grade 6, Unit 2, Lesson 7, Activity 25: Unit Project: Hands-on Engineering: Applying Force, students develop a solution to a problem by utilizing parts of other solutions. They design two possible solutions to the given problem and are asked to compare with other teams. Then, students identify pros and cons of each solution to make adjustments as needed in order to meet the criteria.

• ETS1.B-M4. In Grade 7, Unit 6, Lesson 4, Activity 11: Burning the Fabric, students use questions about what could cause the burning of the Hindenburg from the previous lesson (hydrogen, fabric) and video data of fabric burning to create additional questions that need answering. The videos present three models that are burned: one covered with plain fabric, one covered with fabric painted with three coats of aluminum like the bottom of the Hindenburg, and the third fabric painted with iron oxide and aluminum like the upper half of the Hindenburg. Students collect data from these tests and then develop a claim and construct an explanation. Lastly, students explore multiple facets of what they have figured out from both the model of burning hydrogen and the model of burning fabric to help them think about what they still need to investigate.

• ETS1.C-M1. In Grade 6, Unit 3, Lesson 6, Activity 20: Unit Project: Unwanted Frost on the Window, students are presented with the problem of ice forming on the interior side of windows. After discussing as a class and reviewing their knowledge on heat transfer and changes of state, students brainstorm ideas for why the ice is forming and, with pairs or in small groups, brainstorm possible solutions to keep this from happening. Using various criteria, they rate the possible solutions and construct an explanation for which solution they would propose based on their evaluations.

• ETS1.C-M2. In Grade 6, Unit 1, Lesson 5, Activity 12: Unit Project: Hands-On Engineering: Defining Design Problem, students use the iterative process of testing the most promising solutions and modify what is proposed based on the test results. After modifying their balloon car, students engage in the iterative design process that would allow their balloon car to win a competitive event.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate the science and engineering practices for developing and using models and all grade-band elements across the series. The materials incorporate all grade-band elements of this SEP across the series. Across the series, students have repeated opportunities to develop and use models; students use elements of this SEP in each grade and across each science discipline, with the elements of MOD-M4 and MOD-M5 used most frequently.

Examples of grade-band elements of Developing and Using Models across the series present in the materials:

• MOD-M1. In Grade 6, Unit 2, Lesson 6, Activity 24: Modeling the Levitating Orb System, students use a rubric as a guide to evaluate their classmates’ models and provide them with meaningful feedback to revise models so that they represents the levitating-orb system more clearly or completely.

• MOD-M2. In Grade 7, Unit 6, Lesson 2, Activity 6: Hands-On Investigation: Electrolysis, students use observations from an investigation of electricity running through water to construct a flowchart model of electrolysis and include what happens when energy is added to the system.

• MOD-M3. In Grade 7, Unit 7, Lesson 5, Activity 16: Kelp and Sea Urchins, students use the model of a kelp forest ecosystem to explain data that is presented about the ecosystem. Then they revise their model to account for the population density presented in the data.

• MOD-M4. In Grade 8, Unit 15, Lesson 2, Activity 6: Setting Boundaries, students watch a video of a volcano erupting in Chile. Based on what they know about earthquakes, students construct an explanation about what could be causing this volcanic eruption that also notes plate movement at different types of boundaries and their effects. They create a model to support their explanation, and then watch and read about ocean trenches to further expand their models.

• MOD-M5. In Grade 8, Unit 15, Lesson 3, Activity 9: Down in the Trenches, students read about ocean floors, specifically ocean mapping and trenches. They note patterns and compare maps of plate tectonics and ocean trenches. Using this information, students draw a model explaining the interaction of the Caribbean and North Atlantic Plates at the Puerto Rico Trench. 

• MOD-M5. In Grade 6, Unit 3, Lesson 4, Activity 13: Kinesthetic Models of Energy Transfer to and from the Refrigerant, students work in two groups where each is given a scenario to develop a model. The materials prompt one group to “develop a kinesthetic demonstration that illustrates any changes in state that occur as refrigerant cycles through an air conditioner and suddenly loses air flow over the coils. The model should show any changes in kinetic energy, thermal energy transfer, volume, and pressure as appropriate." The second group is to “develop a kinesthetic demonstration that illustrates any changes in state that occur as refrigerant leaks from the closed system. The model should show any changes in kinetic energy, thermal energy transfer, volume, and pressure as appropriate." With specific attention to their scenario, each group works together to create simulation models that explain their theories for what caused ice to form on the air conditioner.

• MOD-M6. In Grade 8, Unit 15, Lesson 2, Activity 5: Plate Interactions, students watch a video about the causes of plate movement. They complete an activity with graham crackers and frosting to model different types of tectonic boundaries and plate movement (divergent, transform, and collision plate boundaries). Students note what happens at these boundaries, and then analyze images to compare the unobservable mechanisms of plate boundary movement shown by their model to a 3-D map of the Atlantic Ocean and Caribbean sea. They then discuss how they know the Puerto Rico earthquake could not be the result of a transform boundary.

• MOD-M7. In Grade 8, Unit 15, Lesson 2, Activity 3: Continent Puzzle, students create a map of the world using cut out pieces of paper representing continents on which they draw land features studied in the previous activity. They move the continent pieces around to see if they fit together like a puzzle. Lastly, they read and watch a video about continental drift and write a claim about how the continents formed their current shapes and arrangements. 

• MOD-M7. In Grade 6, Unit 5, Lesson 6, Activity 19: Hands-On Investigation: Nerve Response Speed, students investigate the nerve response speed to sound and sight stimuli. They use the results to develop a flowchart model showing receptor inputs (stimulus), the movement of information along nerve cells, and the resulting outputs (body response to stimulus).

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate the crosscutting concept (CCC) of patterns and all grade-band elements across the series. Elements of patterns are found in all units. Across the series, students have repeated opportunities to engage with the CCC of patterns; students use elements of this CCC in each grade, in each science discipline, and in each unit, commonly using multiple elements of this CCC in each unit. 

Examples of grade-band elements of Patterns present in the materials:

• PAT-M1. In Grade 7, Unit 6, Lesson 3, Activity 9: It’s a Matter of Atoms, students use the macroscopic patterns identified in given chemical reactions related to electrolysis and the burning of hydrogen and methane in order to predict how molecules (atomic-level structure) interact (e.g., reactants and products) due to the burning of propane.

• PAT-M2. In Grade 7, Unit 7, Lesson 3, Activity 9: Sunlight Time, students interpret data from graphs on the seasonal increase in kelp length and carbon content in kelp. They discuss patterns observed in the graphs to explain the relationship between energy from the sun and the flow of matter into kelp to understand the natural system. 

• PAT-M3. In Grade 7, Unit 9, Lesson 2, Activity 4: Analyzing and Interpreting Data for Anchorage and Fairbanks, students identify patterns observed in student-created graphs of temperature and snowfall data and determine what the pattern allows them to conclude about the amount of snow in one place versus another.

• PAT-M4. In Grade 8, Unit 15, Lesson 2, Activity 2: Earthquake Data, students review a map of earthquake occurrence in Puerto Rico. After answering questions, students compare two different maps, explaining how the new information can be used to identify patterns related to aftershocks. Specifically, students are asked: “How can analyzing different maps of a region help you better understand natural events, such as earthquakes?”

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate the crosscutting concept (CCC) of cause and effect and all grade-band elements across the series. Of the three grade-band elements of cause and effect, two are fully incorporated, and one is partially incorporated. Across the series, students have repeated opportunities to engage with this CCC; students use elements of this CCC in each grade, in each science discipline, and in nearly all units. The element most frequently incorporated is CE-M2. 

Examples of grade-band elements of Cause and Effect present in the materials:

• CE-M2. In Grade 7, Unit 10, Lesson 6, Activity 15: Hands-On Investigation: Greenhouse Effect, students create a model, gather data to understand the greenhouse effect, and explain how the results can be used to address the cause for and need to move the starting location of the dogsled race. Students select statements that answer "how do you think an increase in greenhouse gases in the atmosphere will affect the amount of snow in Alaska?” and “how does this contribute to the lack of snow on parts of the dogsled race route?"

• CE-M3. In Grade 7, Unit 8, Lesson 6, Activity 13: Before and After, students compare their predictions for weather with actual conditions and discuss how meteorologists use probability when predicting the weather. 

Example of a grade-band element of Cause and Effect partially present in the materials:

• CE-M1. In Grade 7, Unit 6, Lesson 2, Activity 5: Hydrogen Burning, students explore the conditions necessary for the burning of hydrogen. They use evidence to support or refute the claim that hydrogen was the main cause of the Hindenburg explosion. There is a missed opportunity for students to identify relationships that are correlated and to differentiate between causation and correlation.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate the crosscutting concept of systems and system models and all grade-band elements across the series. Across the series, students have repeated opportunities to engage with this CCC; students use elements of this CCC in each grade and in each science discipline. Elements of this CCC are used in all sixth grade units and less frequently in the other grades. The elements SYS-M1 and SYS-M2 are incorporated more frequently than SYS-M3.

Examples of grade-band elements of Systems and System Models present in the materials:

• SYS-M1. In Grade 6, Unit 3, Lesson 4, Activity 12: How an Air Conditioner Cools, Part 2, students review and analyze models of the various subsystems in an air conditioner and identify how they work together in the larger system. 

• SYS-M2. In Grade 7, Unit 7, Lesson 2, Activity 8: Modeling Photosynthesis, students refine a working model of a kelp forest ecosystem to show the interactions of the components of that ecosystem, including the process of photosynthesis. Student models of photosynthesis show the input components of carbon dioxide, water, and sunlight, resulting in the outputs of oxygen and sugar, and energy and matter flow.

• SYS-M3. In Grade 6, Unit 2, Lesson 1, Activity 5: Gravity at Different Scales, students evaluate the limitations of their model and write about parts of the system they have not fully represented.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate the crosscutting concept of energy and matter and all grade-band elements across the series. Across the series, students have multiple opportunities to engage with this CCC; students use elements of this CCC in each grade and in each science discipline. Students engage with elements of this CCC in two or three units per grade, most frequently in physical science units.

Examples of grade-band elements of Energy and Matter present in the materials:

• EM-M1. In Grade 7, Unit 6, Lesson 4, Activity 13: Hands-On Investigation: Energy Lab, students continue their investigations on chemical reactions to understand how they take in energy or give off energy. They record what they think happened with energy during the Hindenburg explosion and list questions they have related to energy as a result of a demonstration in a previous lesson. Prior to viewing a video clip, students predict the outcome of a chemical reaction involving barium hydroxide octahydrate and solid ammonium chloride and then record observations. Students use provided materials as they plan and conduct an investigation to collect data about how energy changes during chemical reactions.  

• EM-M2. In Grade 8, Unit 15, Lesson 2, Activity 4: Changing Continents, students read about the conditions within the earth that result in either liquid or solid material then observe a demonstration model of the processes that drive the movement of continents.   After proving their initial thoughts as to how plates move, students use their observations to explain how energy transfers in a natural system and how this energy is driving the motion and cycling of matter.

• EM-M3. In Grade 6, Unit 2, Lesson 5, Activity 21: Energy Transfer, students describe where energy is stored, used, and transferred in the junkyard-magnetic-paperclip system and compare the potential energy in this system to the potential energy in a rubber band system.

• EM-M4. In Grade 7, Unit 8, Lesson 3, Activity 6: The Water Cycle, students write a story about the journey of a water droplet in the water cycle. They revisit their stories throughout the activity with prompts to change the scenario (you landed somewhere the air temperature remains below freezing all year or you landed somewhere you were absorbed into the ground). After thinking through these different scenarios, students return to their initial story and add in more information to include how the transfer of energy influences the path water takes as it falls from the sky. They apply their understanding of the water cycle to help them explain what happened in the Superstorm.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate the crosscutting concept of structure and function and all grade-band elements across the series. Across the series, students engage with this CCC in multiple units; students use elements of this CCC in sixth and eighth grade and primarily in life science units. 

Examples of grade-band elements of Structure and Function present in the materials:

• SF-M1. In Grade 8, Unit 12, Lesson 3, Activity 7: Making Melanin, students investigate the complex system of the role of proteins in the development of the pigment melanin. They model the complex and microscopic structures and systems to describe how protein structure can determine their function.

• SF-M2. In Grade 6, Unit 2, Lesson 3, Activity 12: Three-D Maglev Model, students use the engineering process to design a three-dimensional maglev system and take into account the properties of the materials provided. They then explain how the structure of one of the used items provides an important function for the overall system.

The instructional materials reviewed for Grades 6-8 meet expectations that they incorporate NGSS connections to the nature of science (NOS) and engineering (ENG). Across the series, materials incorporate most components and many elements of the grade-band NGSS connections. The NOS and engineering elements are represented and attended multiple times throughout the grade-band units. They are used in correlation with the content and not used as isolated lessons. 

Examples of grade-band connections to NOS elements associated with SEPs present in the materials:

• NOS-VOM-M1 . In Grade 8, Unit 11, Lesson 3, Activity 10: Hands-On Investigation: Rubber Band Sounds, the activity planning document includes instructions for small groups of students to discuss the variety of methods and tools they have used in their investigations, where measurements and observations are collected, and to describe the benefit of using different methods and tools when they plan and carry out investigations.

• NOS-BEE-M1. In Grade 8, Unit 16, Lesson 2, Activity 4: Human Dependence on Water, students analyze data on fisheries in the Gulf of Mexico. Students share how they can use all of this evidence to explain why fisheries are nationally important. The materials guide teachers to support students’ understanding of the use of evidence in scientific explanations by asking why it is important to base explanations on evidence and not opinion.

• NOS-OTR-M1. In Grade 8, Unit 16, Lesson 4, Activity 12: Farming and Extinctions, students reflect on the flow chart and models they made to explain the dead fish in the delta. During this reflection, teachers ask students to share how their understandings have changed throughout the unit when given new evidence. Specifically, teachers ask: “How has the evidence you have gathered from your observations helped you improve your initial mind map?” and “Why is it important to keep revising scientific findings?”

• NOS-OTR-M3. In Grade 8, Unit 12, Lesson 2, Activity 6: Gray or White?, students analyze the structure and function of protein molecules then write questions they have about how the structure of genes and proteins are connected to their functions. Students refine their flowchart models to show how proteins relate to genes and observable traits. After their own revisions, students then discuss in small groups why it is important for scientists to continually revise their understanding.

Examples of grade-band connections to NOS elements associated with CCCs present in the materials:

• NOS-WOK-M1. In Grade 6, Unit 3, Lesson 5, Activity 17: Potential Attraction, students prepare to peer review heat curve models. Materials prompt the teacher to explain the peer review process in science, usually through article publication, where other scientists provide feedback, decide if the methods and data are valid, and determine if it should be published. The teacher provides sentence stems for the students to provide constructive and respectful feedback, and students use this as a way to improve their models. Students who disagree with a comment from others provide an evidence-based argument for not making the revisions.

• NOS-WOK-M2. In Grade 6, Unit 2, Lesson 2, Activity 5: Gravity at Different Scales, the activity planning document includes the discussion prompt, “Why can scientists today still use the work of Newton and Cavendish to understand gravity?” The instructions prompt the teacher to use student responses in guiding them to consider the words law and theory as they apply to gravity.

• NOS-AOC-M1. In Grade 6, Unit 2, Lesson 5, Activity 20: Let it Glow!, the activity planning document includes directions for students to explore and discuss how the nature of science applies to the invention of designed devices, such as batteries and capacitors. Students connect the invention of these devices to the assumption that electric fields and forces operate consistently in different systems.

• NOS-HE-M2. In Grade 6, Unit 3, Lesson 6, Activity 20: Unit Project: Unwanted Frost on the Window, students return to the anchoring phenomenon first presented in the unit. As they have solved the problem of the air conditioner, they help solve the issue of ice forming on the inside of the window. In preparing for this activity, the teacher tells the students that they will continue to work as scientists and engineers, which involves persistence, precision, reasoning, logic, imagination and creativity to solve real-world problems.

• NOS-HE-M3. In Grade 6, Unit 5, Lesson 5, Activity 17: Fuel for Healing, students read a passage about the interaction of organ systems during cellular respiration and identify evidence they could use to strengthen their initial claim. Using habit of mind, tolerance of ambiguity, and openness to new ideas, students share their ideas with peers, who may have differing ideas. Students can change their ideas based upon this interaction with peers.

Examples of grade-band connections to ENG elements associated with CCCs present in the materials:

• ENG-INFLU-M1. In Grade 8, Unit 10, Lesson 8, Activity 21: Constructing Explanations, the activity planning document includes instructions to have students reflect on what they have figured out about the positive and negative consequences of human activity on the health of people and the natural environment.

• ENG-INFLU-M2. In Grade 6, Unit 3, Lesson 6, Activity 20: Unit Project: Unwanted Frost on the Window, students construct an explanation for why the ice is forming on the interior of a window. After creating an explanation for the cause, students brainstorm possible solutions to prevent the ice from forming. Once solutions have been created, students regroup to evaluate them based on the Pugh Matrix. Teachers explain to students that engineers have to account for many factors (needs, research findings, and economics) when designing solutions and one way to capture the criteria and constraints to determine the best solution is through using the Pugh Matrix.

• ENG-INFLU-M3. In Grade 8, Unit 11, Lesson 3, Activity 10: Hands-On Investigation: Rubber Band Sounds, the activity planning document includes instructions to have students reflect on the statement, “Technology use varies over time and from region to region.” Materials include other discussion prompts for teachers to use in follow up to this reflection where students describe the benefits of using different tools with investigations. 

• ENG-INTER-M2. In Grade 7, Unit 8, Lesson 2, Activity 8: Zebra Migration Patterns, students read about scientists investigating how a large zebra population behaved during wet season months when resources varied in their home range. Scientists fitted several female zebras with tracking collars. Along with the collars, GPS technology and satellites were used to monitor the zebras’ exact location. Students discuss in small groups how the collars drive understanding science of zebra behavior and how the science might drive the development of the technology.

• ENG-INTER-M3. In Grade 6, Unit 5, Lesson 2, Activity 4: A Whole New Leg?, students discuss how technologies influence scientists' understanding as to how salamanders have the ability to regrow limbs. They answer one prompt about how the technology led to the knowledge of special cells in the salamander leg and another prompt on how technology allows for information to be presented, for example, through the internet.

Examples of where materials partially incorporate grade-band connections to nature of science and engineering: 

• NOS-AQAW-M3. In Grade 8, Unit 14, Lesson 5, Activity 11: The koa tree and the Kauaʻi fruit fly, students explain the effect of the destruction of the Koa tree for plantation development on the Kauaʻi fruit fly population. Students do not explore how science knowledge is responsible for society’s decisions.

• ENG-INTER-M1. In Grade 6, Unit 5, Lesson 2, Activity 3: Under the Microscopes, students observe microscopic images and discuss how the invention of the microscope has influenced scientific knowledge of living things. Explicit exploration into the development of industries or engineered systems is not included.