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': 'Bone resorption markers are: \nSelect and explain. \nA. Serum propeptide of type I procollagen, B. Osteocalcin, C. Urine total free deoxypyridinoline, D. Free glutamic acid cross linkage.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C. i.e. Urine total free deoxypyridindine', 'role': 'assistant'}]