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
Systemic water fluoridation reduces caries 
Select and explain. 
A. by 25%, B. only on smooth surfaces, C. on smooth surfaces and pit and fissures, D. is possible only in advanced countries
B: only on smooth surfaces
Answer: B: only on smooth surfaces 
Explanation: None