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
Specific gravity of enamel is: 
Select and explain. 
A. 2.1, B. 2.8, C. 3.2, D. 3.4
B: 2.8
Answer: B: 2.8 
Explanation: None