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': 'Posterior border of heart is formed by all except? \nSelect and explain. \nA. Pulmonary artery, B. Left atrium, C. Left ventricle, D. Right  atrium', 'role': 'user'}, {'content': 'Answer: D \nExplanation: From above downwards(Posterior border) :\na.\xa0Pulmonary artery.\nb.\xa0Left atrium.\nc.\xa0Left ventricle.', 'role': 'assistant'}]