During Normal Exhalation,air Leaves the Lungs Because

During normal exhalation,air leaves the lungs because:

A) air currents outside the body draw air out of the lungs
B) the strong chest muscles force air out by squeezing the chest cavity
C) of the elastic recoil of muscles making air pressure greater inside the lungs than outside so it flows outward
D) there is more carbon dioxide inside the lungs than outside,so air flows outward by diffusion