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
According to Schour & Massler the crown completion of both permanent maxillary and mandibular first molars is: 
Select and explain. 
A. 1½  - 2 years, B. 2½ - 3 years, C. 3 - 4 years, D. 4 - 5 years
B: 2½ - 3 years
Answer: B: 2½ - 3 years 
Explanation: None