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
[{'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 aortic knockle', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Radiological features of ASD:- Normal size heart or mild cardiomegaly, normal or enlarged pulmonary artery, pulmonary plethora, enlarged right atrium and ventricle, normal size left atrium, small aortic knob.', 'role': 'assistant'}]