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
[{'content': 'Function of serum albumin is: \nSelect and explain. \nA. Toxin transport, B. Acts as Buffer, C. Drug transport, D. Maintenance of oncotic pressure', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]