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: Radiology
[{'content': 'Cupola sign – \nSelect and explain. \nA. Radiological finding in supine posture for pneumoperitoneum, B. Radiological finding in supine posture for pneumothorax, C. Air in Morrison pouch, D. Both wall of bowel is seen', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Cupola sign is seen in supine film of pneumoperitoneum', 'role': 'assistant'}]