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
EPA and NEERI, which of the element is used? 
Select and explain. 
A. ALF3, B. CaF2, C. NaF, D. SnF2
A: ALF3
Answer: A: ALF3 
Explanation: None