This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Electrocardiography, Subject name: Medicine
[{'content': 'P wave in ECG is due to : \nSelect and explain. \nA. Ventricular depolarization, B. Atrial repolarization, C. Ventricular repolarization, D. Atrial depolarization', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. (d) Atrial depolarizationECG findingSignificanceP waveAtrial DepolarizationQRSVentricular depolarizationT waveVentricular repolarizationU waveDelayed repolarization of papillary musclesPR intervalSpread of impulse from SAN to AVNST segmentIso-electric segment', 'role': 'assistant'}]