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
Retrosternal goiter: 
Select and explain. 
A. Causes stridor, B. Obtains its blood supply from thoracic vessels, C. Characteristically malignant, D. Must be removed by thoracotomy
A: Causes stridor
Answer: A: Causes stridor 
Explanation: None