The respiratory system

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Across
  1. 3. The main respiratory organs
  2. 5. The windpipe
  3. 7. Expands and contracts to allow more air in
Down
  1. 1. Small branches from Bronchi
  2. 2. Small air sacs in the lungs
  3. 4. An air filled space behind the nose
  4. 6. The act of breathing out