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: Surgery
Best investigation for air in peritoneal cavity is ? 
Select and explain. 
A. USG, B. Laparotomy, C. Laparoscopy, D. X-ray abdomen-erect view
D: X-ray abdomen-erect view
Answer: D: X-ray abdomen-erect view 
Explanation: Ans. is 'd' i.e., X-ray abdomen-erect view