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
Stratosphere sign is seen in 
Select and explain. 
A. Pleural effusion, B. Pneumothorax, C. Rib fracture, D. Bronchogenic carcinoma
B: Pneumothorax
Answer: B: Pneumothorax 
Explanation: None