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': 'Radiological sign of ischemic colitis is \nSelect and explain. \nA. Popcorn appearance, B. Thumb print apperance, C. Cobrahead app, D. Inveed 3 sign', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Thumb printing', 'role': 'assistant'}]