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': 'Silhouetting of the left border of heart (silhouette sign positive) on chest radiograph indicates what pathology \nSelect and explain. \nA. Upper lobe, B. Hilar, C. Lingular, D. Lower lobe', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]