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 commonest cause of chronic renal failure is \nSelect and explain. \nA. Chronic glomerulonephritis, B. Chronic pyelonephritis, C. Multiple myeloma, D. Subacute bacterial endocarditis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Commonest cause of chronic renal failure is pyelonephritis.', 'role': 'assistant'}]