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 flap technique procedure which does not increase the width of attached gingiva: \nSelect and explain. \nA. Apically positioned flap, B. Undisplaced flap, C. Fenestration operation, D. Free gingival graft', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]