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
In topical fluoride application, maximum benefit is
derived when the tooth surface is treated for: 
Select and explain. 
A. 15 seconds, B. 30 seconds, C. 1 minute, D. 4 minutes
D: 4 minutes
Answer: D: 4 minutes 
Explanation: None