The Bicarbonate Buffer System Would Not Work Very Well in the Human

The bicarbonate buffer system would not work very well in the human body if not for the action of the respiratory system,which ___________.

A) supplies the buffer system with CO₂
B) supplies the buffer system with O₂
C) expels HCO₃^- produced by the buffer system
D) expels H⁺ produced by the buffer system
E) expels CO₂ produced by the buffer system