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
Periodontal surgery is most difficult to carry out in 2nd molar distally due to: 
Select and explain. 
A. Lack of sufficient attached gingiva., B. Presence of bulbous fibrous tissue over tuberosity and retromolar pad., C. Both, D. None
C: Both
Answer: C: Both 
Explanation: None