This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
Best investigation for air in peritoneal cavity is 
Select and explain. 
A. USG, B. CT, C. Xray abdomen erect view, D. Laproscopy
C: Xray abdomen erect view
Answer: C: Xray abdomen erect view 
Explanation: free gas under the diaphragm is best shown on an erect chest x-ray or x ray abdomen. If the patient is too ill for an erect film, a lateral decubitus film is done.