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
Hardest vital tissue among the following is: 
Select and explain. 
A. Enamel, B. Dentin, C. Cementum, D. None
B: Dentin
Answer: B: Dentin 
Explanation: Dentin is the hardest vital tissue, while the enamel is the hardest non-vital tissue.