This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy and physiology of bone and fracture healing, Subject name: Orthopaedics
which of the following is a Bone resorption marker is ? 
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: Deoxypyridinoline (DPD) in urine, which reflects systemic bone resorption, is considered most useful for assessing the effects of osteoporosis treatment. <a href=" osteocalcin, Serum type 1 procollagen</a> are bone formation markers ref : maheswari book of ohopedics 9th ed