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
Earliest sign of left atrial hyperophy is: 
Select and explain. 
A. Posterior displacement of esophagus, B. Widening of carinal angle, C. Upward displacement of left bronchus, D. Double contour of right border of hea
A: Posterior displacement of esophagus
Answer: A: Posterior displacement of esophagus 
Explanation: Ans. Posterior displacement of esophagus