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
Scabbard Trachea; True is? 
Select and explain. 
A. Flattening of trachea, B. Caused by lateral compression by swellings, C. Caused by lateral compression by tumors, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: SCABBARD (SABER-SHEATH) TRACHEA

Flattening of trachea caused by lateral compression by swellings or tumors.
Causes: Carcinoma thyroid, thyroiditis, carcinoma larynx, goitre.