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': "Not a Radiological sign of Crohn's disease \nSelect and explain. \nA. String sign of Kantor, B. Thumb printing, C. Creeping fat sign, D. Cobble stone appearance", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Thumb printing - mucosal edema seen in ischaemic colitis > Ulcerative colitis.', 'role': 'assistant'}]