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: Dental
[{'content': 'When osteoblast lay new bone from outside to inside in a osteon, the active formation area is called: \nSelect and explain. \nA. Haversion cone, B. Filling cone, C. Cutting cone, D. Howships cone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]