This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Radiology
Earliest sign of left atrial enlargement is - 
Select and explain. 
A. Posterior displacement of esophagus, B. Widening of carinal angle, C. Elevation of left bronchus, D. Double shadow of right border
C: Elevation of left bronchus
Answer: C: Elevation of left bronchus 
Explanation: Left atrial enlargement presents radiologically with elevation of left main bronchus which is the earlier feature ,splaying or widening of carina ,indentation and displacement of oesophagus posteriorly , double contour / shadow / density or double right hea border and prominent left atrial appendage.