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
Which one of the following is the level of residual free chlorine recommended for swimming pool water disinfection ? 
Select and explain. 
A. 0.5 mgilitre, B. 0.8 mg/litre, C. 1 mg/litre, D. 5 mg/litre
C: 1 mg/litre
Answer: C: 1 mg/litre 
Explanation: Ans. is 'c' i.e., I mg/lit