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': 'Hat sign on double contrast barium enema is seen in – \nSelect and explain. \nA. Ulcer, B. Polyp, C. Carcinoma, D. Diverticulum', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hat sign on barium enema is seen in colonic polyp.', 'role': 'assistant'}]