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': 'Most common age for incidence of gingivitis in children \nSelect and explain. \nA. 1 - 3 yrs, B. 11 - 13 yrs, C. 6 - 7 yrs, D. 2 - 7 yrs', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]