This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory, Subject name: Medicine
A 25-year-old man presented to the emergency medicine department with acute onset sharp pain and dyspnea. His chest X-ray (CXR) is given here. What is the diagnosis? 
Select and explain. 
A. Pleural effusion, B. Pulmonry embolism, C. Hydropneumothorax, D. Spontaneous pneumothorax
D: Spontaneous pneumothorax
Answer: D: Spontaneous pneumothorax 
Explanation: ANS. D