Lets solve a crossword puzzle.

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Across
  1. 1. controls the body
  2. 4. filters waste from the body
  3. 6. harmful addition to air
  4. 8. helps to digest food
Down
  1. 2. process of breathing in and out
  2. 3. connects nose to lungs
  3. 5. many birds lay these
  4. 7. helps birds to find and eat food