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': "Pipe stern colon is seen in: \nSelect and explain. \nA. Ulcerative colitis, B. Carcinoma colon, C. Crohn's disease, D. Whipple's disease", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Ulcerative colitis', 'role': 'assistant'}]