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': 'The best investigation for cardiac tamponade is: \nSelect and explain. \nA. 2-D echocardiography, B. Real time echocardiography, C. Ultrasound, D. M-mode echocardiography', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. 2-D echocardiography', 'role': 'assistant'}]