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
X-ray sign of pneumoperitoneum 
Select and explain. 
A. Steeple sign, B. Rigler's sign, C. Golden 'S' sign, D. 'Bird of prey' sign
B: Rigler's sign
Answer: B: Rigler's sign 
Explanation: Rigler's sign - bowel wall outlined by intraluminal and free peritoneal gas.