Carbon Dioxide Crosses the Plasma Membrane by Simple Diffusion

Carbon dioxide crosses the plasma membrane by simple diffusion. The rate at which carbon dioxide enters the cell is determined by the

A) amount of energy being produced by the cell.
B) amount of transport protein in the membrane.
C) concentration of carbon dioxide on each side of the membrane.
D) amount of oxygen being exported from the cell.
E) amount of carbon dioxide outside of the cell.