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
Basic metabolic unit of bone is: 
Select and explain. 
A. Osteon, B. Osteoblast, C. Osteocyte, D. Osteoclast
A: Osteon
Answer: A: Osteon 
Explanation: None