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': 'Concentration of fluoride in community water supplies as proposed by WHO in 1969 was- \nSelect and explain. \nA. 1.5 ppm, B. 1 ppm, C. 0.5 ppm, D. 2 ppm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In 1969,\xa0WHO\xa0advocated that 1 ppm of fluoride in community water supplies was a practical and effective public health measure.', 'role': 'assistant'}]