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': 'Scabbard Trachea; True is? \nSelect and explain. \nA. Flattening of trachea, B. Caused by lateral compression by swellings, C. Caused by lateral compression by tumors, D. All of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: SCABBARD (SABER-SHEATH) TRACHEA\n\nFlattening of trachea caused by lateral compression by swellings or tumors.\nCauses: Carcinoma thyroid, thyroiditis, carcinoma larynx, goitre.', 'role': 'assistant'}]