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': 'The most sensitive index for renal tubular function is: \nSelect and explain. \nA. Specific gravity of urine, B. Blood urea, C. GFR, D. Creatinine clearance', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Specific gravity of urineThe main function of renal tubules is concentration of urine and this can be measured by specific gravity of urine.', 'role': 'assistant'}]