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
First compound added in Grand rapids was: 
Select and explain. 
A. Calcium fluoride., B. Sodium fluoride, C. Stennous fluoride., D. APF
B: Sodium fluoride
Answer: B: Sodium fluoride 
Explanation: None