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': 'Gingivitis is at its peak in children at age: \nSelect and explain. \nA. 3 - 4 years, B. 6 - 7 years, C. 11 - 13 years, D. 15 -18 years', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]