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': 'Defluoridation of water is carried out using: \nSelect and explain. \nA. Chlorine, B. Phosphate, C. Calcium, D. Ozone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Some areas may contain excessive fluoride levels in drinking water. Defluoridation is carried out using phosphates. Ref: Park 21st edition page: 672.', 'role': 'assistant'}]