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': 'There are two normal children of the same age and sex. In one, all the permanent teeth except the third molars have erupted. In the other, no permanent canines or premolars have erupted. How old are these children? \nSelect and explain. \nA. 7 years, B. 9 years, C. 11 years, D. 13 years', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]