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: Unknown
[{'content': 'Most metabolically active part in bone is \nSelect and explain. \nA. Cortical bone, B. Cancellous bone, C. Periosteal surface, D. Endosteal surface', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Endosteum is the most metabolically active part in bone', 'role': 'assistant'}]