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': 'Structures preserved in modified radical neck dissection are all except: \nSelect and explain. \nA. Accessory nerve, B. Sternocleidomastoid muscle, C. Submandibular gland, D. Internal jugular vein', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]