35 POINTS!!!!!!
In the image above of an alveolus, what is the identity of the two visible tissue layers labeled C and D.

A. C = inner wall of alveolar sac; D = outer wall of alveolar sac
B. C = inner wall of alveolar sac; D = outer capillary wall
C. C = outer wall of alveolar sac; D = outer capillary wall
D. C = inner capillary wall; D = outer capillary wall