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
Inverted "3" sign seen in 
Select and explain. 
A. Ampullary Ca, B. Insulinoma, C. Ca. head pancreas, D. Ca. stomach
C: Ca. head pancreas
Answer: C: Ca. head pancreas 
Explanation: None