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': 'First compound added in Grand rapids was: \nSelect and explain. \nA. Calcium fluoride., B. Sodium fluoride, C. Stennous fluoride., D. APF', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]