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': 'Method of choice for purification of highly polluted water on a large scale is \nSelect and explain. \nA. Boiling, B. Super chlorination followed by dechlorination, C. Chlorination, D. Ultraviolet light treatment', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]