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 internal bevel incision of a periodontal flap: \nSelect and explain. \nA. is directed to the base of the pocket, B. removes the keratinized tissue completely, C. is a vertical incision, D. remove the lining of the pocket wall', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]