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': 'Jack stone calculi are made up of \nSelect and explain. \nA. Ammonium urate, B. Uric acid, C. Struvite, D. Calcium oxalate', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Jack stone calculi are seen in bladder formed by calcium oxalate.', 'role': 'assistant'}]