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
Stage IV of ANUG according to Hornig and Cohen is characterized by 
Select and explain. 
A. 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
B: Necrosis extending to the attached gingiva
Answer: B: Necrosis extending to the attached gingiva 
Explanation: None