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
Brudevold's solution contains: 
Select and explain. 
A. 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
D: 2 percent sodium fluoride in 0.1 M orthophosphoric acid
Answer: D: 2 percent sodium fluoride in 0.1 M orthophosphoric acid 
Explanation: None