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': 'All are seen in left atrium enlargement except: \nSelect and explain. \nA. Posterior displacement of the oesophagus on barium meal, B. Straightening of the left main hronchus, C. A double shadow of right atrium, D. Retrosternal lucency on lateral film', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. Retrosternal lucency on lateral film', 'role': 'assistant'}]