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
When osteoblast lay new bone from outside to inside in a osteon, the active formation area is called: 
Select and explain. 
A. Haversion cone, B. Filling cone, C. Cutting cone, D. Howships cone
B: Filling cone
Answer: B: Filling cone 
Explanation: None