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
Main body of dentin is formed by 
Select and explain. 
A. Intertubular dentin, B. Mantle dentin, C. Circumpulpal dentin, D. Secondary dentin
A: Intertubular dentin
Answer: A: Intertubular dentin 
Explanation: None