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 can be classified as following, except: 
Select and explain. 
A. Substernal., B. Plunging., C. Nodular., D. Intra-thoracic.
C: Nodular.
Answer: C: Nodular. 
Explanation: None