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': 'EPA and NEERI, which of the element is used? \nSelect and explain. \nA. ALF3, B. CaF2, C. NaF, D. SnF2', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]