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
Percentage of Phosphoric acid where Dicalcium phosphate
monohydrate is formed that cannot be rinsed off. 
Select and explain. 
A. 25%, B. 37%, C. 50%, D. 85%
A: 25%
Answer: A: 25% 
Explanation: None