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': 'Angle of tracheal bifurcation is increased in enlargement of: \nSelect and explain. \nA. Right ventricle, B. Left ventricle, C. Right atrium, D. Left atrium', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. Left atrium', 'role': 'assistant'}]