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': 'Guided tissue regeneration (GTR) is done in: \nSelect and explain. \nA. Vestibular deepening procedures, B. Frenectomy, C. Flap surgeries, D. Gingivectomy', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]