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': 'Inverted "3" sign seen in \nSelect and explain. \nA. Ampullary Ca, B. Insulinoma, C. Ca. head pancreas, D. Ca. stomach', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]