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': "String sign is seen in: \nSelect and explain. \nA. Crohn's disease, B. TB of the ileocaecal region, C. Idiopathic hyperophic pyloric stenosis, D. All of the above", 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. All of the above', 'role': 'assistant'}]