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: Pharmacology
Major mechanism of transport of drugs across biological membranes is by ? 
Select and explain. 
A. Passive diffusion, B. Facilitated diffusion, C. Active transport, D. Endocytosis
A: Passive diffusion
Answer: A: Passive diffusion 
Explanation: None