Which feature of the alveoli most directly speeds up diffusion of gases?

1. Rate of diffusion rises as the distance the gas must travel falls. 2. Alveolar walls are one cell thick, and the capillary wall beside them is also one cell thick. 3. That gives a diffusion path of about two cells between air and blood. 4. A thick or rigid wall would lengthen that path and slow exchange. 5. The lining is moist, not dry, because gases must dissolve before they diffuse. _Source: NECTA ACSEE 2023 Biology 133/1, Question 2: Gaseous Exchange and Respiration_