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: Unknown
20-years-old male with history of RTA presents with breathlessness.  Stratosphere sign on USG with M mode is seen.  What is the probable diagnosis? 
Select and explain. 
A. Hemothorax, B. Pneumothorax, C. Cardiac tamponade, D. Pulmonary embolism
B: Pneumothorax
Answer: B: Pneumothorax 
Explanation: Radiological signs in trauma (eFAST)