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
Function of serum albumin is: 
Select and explain. 
A. Toxin transport, B. Acts as Buffer, C. Drug transport, D. Maintenance of oncotic pressure
D: Maintenance of oncotic pressure
Answer: D: Maintenance of oncotic pressure 
Explanation: None