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': 'Which of the following are hardest renal stones \nSelect and explain. \nA. Calcium Oxalate, B. Struvite, C. Xanthine, D. Cysteine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer- A. Calcium OxalatePure calcium phosphate stones and calcium monohydrate stones are the densest per volume ofstone.Among the given options calcium oxalate stones are densest (hardest).', 'role': 'assistant'}]