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
Fluoride is least effective in which area: 
Select and explain. 
A. Cusp, B. Pits and fissures, C. Buccal areas, D. Palatal area
B: Pits and fissures
Answer: B: Pits and fissures 
Explanation: None