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': '0.2% NaF mouth rinse is recommended \nSelect and explain. \nA. Once daily, B. By weekly, C. Fortnightly, D. Twice weekly', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]