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': 'In a patient with head injury, unexplained hypotension warrants evaluation of: \nSelect and explain. \nA. Upper cervical spine, B. Lower cervical spine, C. Thoracic spine, D. Lumbar spine', 'role': 'user'}, {'content': "Answer: C \nExplanation: High thoracic or cervical cord transection causes hypotension and bradycardia due to functional sympathectomy (sometimes with Horner syndrome). Ref: Harrison's Principles of Internal Medicine, 15th Edition, Page 2441; Surgery: Basic Science and Clinical Evidence By Jeffrey A. Noon, Philip S. Barie, Randall Bollinger, 2008, Page 314", 'role': 'assistant'}]