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': 'Rim sign in IVP is seen in – \nSelect and explain. \nA. Polycystic kidney, B. Hydronephrosis, C. Chronic pyelonephritis, D. Hypemephroma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Two most important causes of rim sign on nephrogram are -\n\t(i) Hydronephrosis (chronic obstruction), and\n\t(ii) Renal artery occulusion.', 'role': 'assistant'}]