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': 'Nalgonda Technique for defluoridation of water does not include addition of? \nSelect and explain. \nA. Line, B. Alum, C. Bleaching powder, D. Barium sulfate', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Nalgonda Technique involves addition of\n\nLime\nAlum\nBleaching powder', 'role': 'assistant'}]