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': 'Inveed "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: Answer is \'c\' i.e. Ca head of pancreas "Ca of the head of the pancreas frequently causes changes in the duodenal loop. There may be widening of the duodenal loop, a double contour, irregularity of the inner border, and stricturing or distoion of the valvulae conniventes. The reversed \'3\' sign of Frostberg is often quoted as being characteristic, but is an infrequent finding." - Grainger', 'role': 'assistant'}]