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: Medicine
[{'content': 'The most specific marker of renal function is - \nSelect and explain. \nA. Creatinine clearance, B. Insulin clearance, C. Blood area, D. Serum creatinine', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]