This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of the following is responsible for the movement of O2 from the alveoli into the blood in the pulmonary capillaries? 
Select and explain. 
A. Active transport, B. Filtration, C. Facilitated diffusion, D. Passive diffusion
D: Passive diffusion
Answer: D: Passive diffusion 
Explanation: Gases diffuse from the alveoli to the blood in the pulmonary capillaries or vice versa across the thin alveolocapillary membrane made up of the pulmonary epithelium, the capillary endothelium, and their fused basement membranes.