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
[{'content': 'Best investigation for air in peritoneal cavity is \nSelect and explain. \nA. USG, B. CT, C. Xray abdomen erect view, D. Laproscopy', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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.', 'role': 'assistant'}]