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
"Westermark sign" is seen in: 
Select and explain. 
A. Pneumomediastinum, B. Pulmonary adenocarcinoma, C. Pulmonary embolism, D. Pancoast syndrome
C: Pulmonary embolism
Answer: C: Pulmonary embolism 
Explanation: "Westermark Sign" is focal oligemia seen distal to arterial block, on chest X-ray.