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 concentration of free chlorine in drinking water at the end of one hour (mg/L) is – 
Select and explain. 
A. 0.1, B. 0.5, C. 1, D. 1.5
B: 0.5
Answer: B: 0.5 
Explanation: None