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
The following study was conducted to check anticariogenic effect of fluoride EXCEPT 
Select and explain. 
A. Dutch study, B. Newburg-Kingston study, C. Evauston-Oak study, D. Shoe-Leather survey
D: Shoe-Leather survey
Answer: D: Shoe-Leather survey 
Explanation: None