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': 'The Fluoride form that has to be freshly prepared before use is: \nSelect and explain. \nA. NaF, B. SnF, C. APF solution, D. APF gel', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]