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
Fluoride supplement for a 3-year old child living in an area with fluoride content of 0.25 ppm is: 
Select and explain. 
A. 0.25 mg, B. 0.5 mg, C. 0.75 mg, D. 1 mg
B: 0.5 mg
Answer: B: 0.5 mg 
Explanation: None