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
Dentin formed through out the life is 
Select and explain. 
A. Sclerotic dentin, B. Secondary dentin, C. Reparative dentin, D. All of the above
B: Secondary dentin
Answer: B: Secondary dentin 
Explanation: None