Increasing the number of stomata per unit surface area of a leaf when atmospheric CO₂ levels decline is most analogous to a human

A) breathing faster as atmospheric CO₂ levels increase.
B) putting more red blood corpuscles (RBCs) into circulation when atmospheric O₂ levels decline.
C) removing RBCs from circulation when atmospheric O₂ levels increase.
D) breathing more slowly as atmospheric O₂ levels increase.