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': 'Angular bone defects are classified \nSelect and explain. \nA. According to the depth of the pockets, B. According to the number of walls involved, C. According to type of pockets, D. According to the number of walls remaining', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]