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': 'X-ray features of ASD are all except - \nSelect and explain. \nA. Right atrial enlargement, B. Left atrial enlargement, C. Pulmonary plethora, D. Small aoic knockle', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Characteristic features of ASD include enlarged hea,Right Atrium,Right Ventricle,Pulmonary Aery and Pulmonary Vein with Normal Left atrium and Left ventricle and decreased aoa and SVC.', 'role': 'assistant'}]