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': 'The recommended concentration of fluoride in a community water supply is: \nSelect and explain. \nA. 0.1 ppm, B. 0.5 ppm, C. 1.0 ppm, D. 2.0 ppm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Fluoridation is the adjustment of water supply to a fluoride content such that reduction\xa0of 50 to 70% in dental caries would occur without damage to teeth or other structures.\nIn 1958, WHO produced the first report by an expert committee on water fluoridation (TRS 146) and concluded that drinking water containing about 1 ppm fluoride had\xa0marked caries - preventive action and that controlled fluoridation of drinking water was a practicable and effective public health measure.\n\nEssentials of preventive and community dentistry\nSoben Peter\n5th edition\npage no. 265', 'role': 'assistant'}]