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
[{'content': 'Double shadow behind right atrium and straightening of left main bronchus indicates - \nSelect and explain. \nA. Right atrium enlargement, B. Right ventricle enlargement, C. Left atrium enlargement, D. Left ventricle enlargement', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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', 'role': 'assistant'}]