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
Repeated application of sodium or potassium flouride to teeth of children significantly reduced their caries prevalence. This was first demonstrated by 
Select and explain. 
A. Knutson, B. Bibby, C. Muhler, D. Dean
B: Bibby
Answer: B: Bibby 
Explanation: None