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: Orthopaedics
[{'content': 'Which of the changes occur in bone growth - \nSelect and explain. \nA. Increased acid phosphatase, B. Increased urinary calcium, C. Increased bone nucleotidase, D. Increased osteocalcin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: During bone growth and development, bone formation, i.e. osteoblastic activity predominates → Osteocalcin is used as sensitive and specific serum marker for osteoblastic activity.', 'role': 'assistant'}]