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
[{'content': 'One tablet of chlorine is effective to disinfect how much quantity of water \nSelect and explain. \nA. 5 L, B. 20 L, C. 10 L, D. 30 L', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]