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
One tablet of chlorine is effective to disinfect how much quantity of water 
Select and explain. 
A. 5 L, B. 20 L, C. 10 L, D. 30 L
B: 20 L
Answer: B: 20 L 
Explanation: None