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': 'The time taken for primary tooth root completion after eruption: \nSelect and explain. \nA. 3 years, B. 1 year, C. 2 years, D. 1 month', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]