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 is related to ? \nSelect and explain. \nA. Fluorine, B. Chlorine, C. Nitrate, D. Nitrites', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]