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': 'Use of floss in healthy mouth is recommended: \nSelect and explain. \nA. Not recommended, B. Once daily, C. Each time after meals, D. Twice daily', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]