This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
Indicators of osteoblastic activity - 
Select and explain. 
A. Alkaline phosphatase, B. Osteocalcin, C. Hydroxyproline, D. Acid phosphatase
A: Alkaline phosphatase
Answer: A: Alkaline phosphatase 
Explanation: bone formation indicator is alkaline phosphatase ( Harrison 17 pg 2382)