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: Unknown
[{'content': 'Hallmark feature shown in ECG is ? \nSelect and explain. \nA. Prominent U wave, B. Inverted T wave, C. Bizarre QRS wave, D. Osborn J wave', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]