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 signs of crohn's disease – \nSelect and explain. \nA. String sign of Kantor, B. Pipestem appearance, C. Pseudopolyp, D. Backwash ileitis", 'role': 'user'}, {'content': "Answer: A \nExplanation: String sign of Kantor is seen in Crohn's disease.\nOther three options (Pipestem appearance, pseudopolyp, Backwash ileitis) are features of UC.", 'role': 'assistant'}]