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
Additional period required for enamel calcification after eruption into oral cavity 
Select and explain. 
A. 1 yr, B. 2 yr, C. 3 yr, D. 4 yr
B: 2 yr
Answer: B: 2 yr 
Explanation: None