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: Radiology
[{'content': 'Best method to reduce radiation caries is: \nSelect and explain. \nA. 1% neutral sodium fluoride., B. 2% neutral sodium fluoride., C. 0.5% neutral sodium fluoride., D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The best method to reduce radiation caries is application of viscous 1% neutral sodium fluoride gel at regular intervals.', 'role': 'assistant'}]