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': 'Stage IV of ANUG according to Hornig and Cohen is characterized by \nSelect and explain. \nA. Necrosis of the tip of interdental papilla, B. Necrosis extending to the attached gingiva, C. Necrosis exposing alveolar bone, D. Necrosis perforating skin of cheek', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]