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
Double shadow behind right atrium and straightening of left main bronchus indicates - 
Select and explain. 
A. Right atrium enlargement, B. Right ventricle enlargement, C. Left atrium enlargement, D. Left ventricle enlargement
C: Left atrium enlargement
Answer: C: Left atrium enlargement 
Explanation: Left atrial enlargement presents radiologically with elevation of left main bronchus ( earliest feature ) ,splaying or widening of carina ,displacement of oesophagus posteriorly ,double Right hea border and prominent left atrial appendage