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 WHO index for fluorosis is based on: 
Select and explain. 
A. Dean's index, B. McKay's index, C. Community Fluorosis index, D. Public Health fluorosis index
A: Dean's index
Answer: A: Dean's index 
Explanation: None