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
Knutson's technique of fluoride application is done the following years: 
Select and explain. 
A. 3, 7, 11, 13, B. 2, 6, 10, 16, C. 8, 13, 18, 31, D. 2,	7,	11,	18
A: 3, 7, 11, 13
Answer: A: 3, 7, 11, 13 
Explanation: None