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': 'The primary etiologic factor in the development of furcation defect is \nSelect and explain. \nA. Calculus, B. Plaque, C. Cemental caries, D. Root infection', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]