Carbon dioxide, the waste product of respiration, is excreted mainly by the

  • A. lungs
  • B. kidneys
  • C. liver
  • D. skin

Explanation

CO2 diffuses into the alveoli and is breathed out, so the lungs are the principal organ of its removal. The kidneys handle nitrogenous wastes instead, dividing excretory labour between the two systems.

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