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
The minimum recommended level of residual chlorine in the drinking water is for one hour 
Select and explain. 
A. 0.5 mg/L, B. 0.25 mg/L, C. 1.0 mg/L, D. 2.0 mg/L
A: 0.5 mg/L
Answer: A: 0.5 mg/L 
Explanation: None