This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Radiology
[{'content': 'Stratosphere sign is seen in \nSelect and explain. \nA. Pleural effusion, B. Pneumothorax, C. Rib fracture, D. Bronchogenic carcinoma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]