This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Surgery
[{'content': "X-ray sign of pneumoperitoneum \nSelect and explain. \nA. Steeple sign, B. Rigler's sign, C. Golden 'S' sign, D. 'Bird of prey' sign", 'role': 'user'}, {'content': "Answer: B \nExplanation: Rigler's sign - bowel wall outlined by intraluminal and free peritoneal gas.", 'role': 'assistant'}]