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: Dental
[{'content': 'Nalgonda tech is used for \nSelect and explain. \nA. Deflouridation, B. fluoridation, C. Purification of water, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]