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: Surgery
[{'content': 'Following is true of Pyonephrosis except - \nSelect and explain. \nA. Commonly associated with Renal calculi, B. Always unilateral, C. Is a complication of Hydronephrosis, D. Follows acute pyelonephritis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]