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': 'Calcification of all teeth except last molars are completed by: \nSelect and explain. \nA. 2 years, B. 4 years, C. 6 years, D. 8 years', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]