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': 'Most common cause of widening of C loop of duedenum \nSelect and explain. \nA. Pancreatitis, B. Carcinoma head of pancreas, C. Choledochal cyst, D. Retroperitoneal masses', 'role': 'user'}, {'content': 'Answer: B \nExplanation: M/c cause - Carcinoma head of pancreas.', 'role': 'assistant'}]