Grade 4 topic 2 review puzzle

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Across
  1. 4. materials that formed as ancient plants and animals decayed underground
  2. 5. a device that spins as the gas flows and changes the heat energy of the steam into energy of motion
  3. 8. a fossil fuel that occurs in the gas state
  4. 9. where gases from the plant pass through a substance that reduces the amount of pollutants that get into the air
  5. 11. light
  6. 12. the release of substances into the environment
  7. 14. found in underground rocks, what most nuclear power plants use
  8. 15. harmful substance
  9. 17. Using the energy of moving water
Down
  1. 1. a hard, black substance
  2. 2. heat energy obtained from beneath the Earth's surface
  3. 3. a material that releases energy as heat when it burns
  4. 6. an original
  5. 7. the unstable elements that produce energy in power plants
  6. 10. the process of burning a fuel to produce heat
  7. 13. stores chemical energy and can convert that energy into electrical energy
  8. 15. a liquid fossil fuel formed by the decay of ancient plants and animals
  9. 16. a device that changes energy of motion into electrical energy