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': '1PPM of water flouride reduces caries experience by 60%, this was discovered by: \nSelect and explain. \nA. Mckay, B. Dean, C. Churchill, D. WHO', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]