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
[{'content': 'Typhoid perforation is diagnosed by- \nSelect and explain. \nA. Plain X-ray of abdomen in erect posture, B. Rectal examination, C. Gastric aspiration, D. Barium enema', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]