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': "Knutson's technique of fluoride application is done the following years: \nSelect and explain. \nA. 3, 7, 11, 13, B. 2, 6, 10, 16, C. 8, 13, 18, 31, D. 2,\t7,\t11,\t18", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]