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
[{'content': '"Westermark sign" is seen in: \nSelect and explain. \nA. Pneumomediastinum, B. Pulmonary adenocarcinoma, C. Pulmonary embolism, D. Pancoast syndrome', 'role': 'user'}, {'content': 'Answer: C \nExplanation: "Westermark Sign" is focal oligemia seen distal to arterial block, on chest X-ray.', 'role': 'assistant'}]