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 not removed in radical neck dissectiona) X nerveb) X1 nervec) Tail of parotidd) Parotid and post-auricular nerve \nSelect and explain. \nA. acd, B. bc, C. bd, D. ac', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]