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: Surgery
[{'content': 'The surgical procedure of choice for skeletal class 2 malocclusion due to retrognathic Mandible is \nSelect and explain. \nA. Le fort I osteotomy, B. Advancement genioplasty, C. BSSO set back of mandible, D. BSSO advancement of mandible', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]