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: Social & Preventive Medicine
Acceptable fluoride concentration in drinking water is 
Select and explain. 
A. 4 ppm, B. 2 ppm, C. 3 ppm, D. 1 ppm
D: 1 ppm
Answer: D: 1 ppm 
Explanation: None