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': 'A dental surgeon appointed in a rural health centre reports an increased incidence of dental caries in the people of that area. Research team confirmed that water supply of that area is deficient in \nSelect and explain. \nA. Chloride, B. Sodium, C. Calcium, D. Fluoride', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]