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: Radiology
[{'content': 'Air bronchogram on chest Xray denotes \nSelect and explain. \nA. Intrapulmonary lesion, B. Extrapulmonary lesion, C. Intrathoracic lesion, D. Extrathoracic lesion', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A solitary pulmonary nodule (SPN) or coin lesion is a mass in the lung smaller than 3 centimeters in diameter.\nIt can be an incidental finding found in up to 0.2% of chest X-rays and around 1% of CT scans.', 'role': 'assistant'}]