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
Bone resorption markers are: 
Select and explain. 
A. Serum propeptide of type I procollagen, B. Osteocalcin, C. Urine total free deoxypyridinoline, D. Free glutamic acid cross linkage.
C: Urine total free deoxypyridinoline
Answer: C: Urine total free deoxypyridinoline 
Explanation: C. i.e. Urine total free deoxypyridindine