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
In school water fluoridation, amount of F used is: 
Select and explain. 
A. 0.7-1.2 ppm, B. 1.6-3 ppm, C. 3-4 ppm, D. 12 ppm
C: 3-4 ppm
Answer: C: 3-4 ppm 
Explanation: None