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
The internal bevel incision of a periodontal flap: 
Select and explain. 
A. 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
D: remove the lining of the pocket wall
Answer: D: remove the lining of the pocket wall 
Explanation: None