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
Recommended fluoride levels in the water should be 
Select and explain. 
A. <2 ppm, B. <1 ppm, C. <1 g/litre, D. <2 g/litre
B: <1 ppm
Answer: B: <1 ppm 
Explanation: None