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 % reduction in caries to be expected by the application of neutral fluoride solution is: \nSelect and explain. \nA. 20%, B. 20-50%, C. variable, D. 10%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]