How are carbon dioxide and oxygen exchanged in the lungs?
A. Large blood vessels constrict and enlarge near the the lung tissue so gases can be exchanged.
B. Carbon dioxide and oxygen are exchanged in the aorta.
C. Small blood vessels pass next to the air sacs of the lung, gases are exchanged across a thin membrane.

D. The walls of the arteries thicken, harden, and lose their elasticity so that oxygen can pass through them.