This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Physiology
Oxygen comes from alveoli to blood by- 
Select and explain. 
A. Diffusion, B. Receptor mediated, C. Active transport, D. Osmosis
A: Diffusion
Answer: A: Diffusion 
Explanation: Ans. (a) Diffusion(Ref: Ganong, 25th ed/p.640)Diffusion means movement of molecules from area of high concentration to area of low concentrationGas exchange in lungs happens in the form of diffusion in lungs