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': 'Root completion of permanent mandibular tooth occurs \nSelect and explain. \nA. 1-1 ½ year after eruption, B. 2-3 year after eruption, C. 6 months after eruption, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]