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': 'Action of chlorine in water is through: \nSelect and explain. \nA. Hypochlorous acid, B. HCL, C. Both of the above, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Hypochlorous acid', 'role': 'assistant'}]