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
[{'content': 'Systemic water fluoridation reduces caries \nSelect and explain. \nA. by 25%, B. only on smooth surfaces, C. on smooth surfaces and pit and fissures, D. is possible only in advanced countries', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]