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: Radiology
[{'content': "Which of the following is diagnostic of the 'Rim sign' in a nephrogram? \nSelect and explain. \nA. Pyelonephritis, B. Hyper nephroma, C. Polycystic kidney, D. Polycystic kidney", 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. Polycystic kidney', 'role': 'assistant'}]