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': 'Periodontal surgery is most difficult to carry out in 2nd molar distally due to: \nSelect and explain. \nA. Lack of sufficient attached gingiva., B. Presence of bulbous fibrous tissue over tuberosity and retromolar pad., C. Both, D. None', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]