If alveolar walls become thick, what will happen to gas exchange?

Correct answer: Diffusion of gases will become slower

The governing concept is diffusion across the respiratory surface. Alveoli normally have very thin, moist walls, so oxygen and carbon dioxide travel across a short distance between air and blood. If the walls become thick, the diffusion distance and resistance increase. Consequently, oxygen enters the blood and carbon dioxide leaves it more slowly, reducing the efficiency of gas exchange. Thus A is correct; the other options concern unrelated or impossible effects.