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
Silhouetting of the left border of heart (silhouette sign positive) on chest radiograph indicates what pathology 
Select and explain. 
A. Upper lobe, B. Hilar, C. Lingular, D. Lower lobe
C: Lingular
Answer: C: Lingular 
Explanation: None