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
[{'content': 'According to Schour & Massler the crown completion of both permanent maxillary and mandibular first molars is: \nSelect and explain. \nA. 1½  - 2 years, B. 2½ - 3 years, C. 3 - 4 years, D. 4 - 5 years', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]