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': 'Percentage of patients with perforated peptic ulcer who show free gas under the diaphragm - \nSelect and explain. \nA. 100%, B. 75%, C. 50%, D. 90%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: • Upright chest x-ray shows free air in about 80% of patients of perforated peptic ulcer.', 'role': 'assistant'}]