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': 'Intra oral vertical ramus osteotomy is done for \nSelect and explain. \nA. Anterior open bite, B. Mandibular advancement, C. Mandibular set back, D. Maxillary deformity', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]