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
Residual chlorine level after swimming pool sanitation 
Select and explain. 
A. >0.5 mg/l, B. >0.7 mg/l, C. >1 mg/l, D. >0.7 ppm
C: >1 mg/l
Answer: C: >1 mg/l 
Explanation: None