Nature

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Across
  1. 2. the number of times that a light wave (or a sound wave or a radio wave) vibrate (moves up and down)
  2. 3. the gases around the world
  3. 6. the smallest unit of a substance, with two or more atoms
  4. 7. a chemical that combines two or more elements
Down
  1. 1. a single living plant, animal, virus, etc.
  2. 4. a series of actions that you take in order to achieve a result
  3. 5. the line where the sky and the land or sea seem to meet