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': 'Periodontitis is usually severe in patients: \nSelect and explain. \nA. Taking phenytoin, B. With defective neutrophils, C. With bruxism, D. With overcrowding', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]