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': 'Which vital structure is preserved during radical dissection - \nSelect and explain. \nA. Vagus nerve, B. Submandibular gland, C. Strenocleidomastoid, D. Internal jugular vein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]