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: Unknown
[{'content': "Below X-ray 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: Pipestem colon is seen in ulcerative colitis\nString sign of Kantor is seen in Crohn 's disease.", 'role': 'assistant'}]