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: Radiology
[{'content': 'Widening of the C loop in X-ray is diagnostic of: \nSelect and explain. \nA. Chronic pancreatitis, B. Carcinoma head of pancreas, C. Periampullary carcinoma, D. Calculi in the ampulla junction', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Carcinoma head of pancreas', 'role': 'assistant'}]