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': "Brudevold's solution contains: \nSelect and explain. \nA. 2 % SnF2, B. 2 % NaF2, C. 1.23 percent sodium fluoride in 0.1 M orthophosphoric acid, D. 2 percent sodium fluoride in 0.1 M orthophosphoric acid", 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]