This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart: Normal Electrocardiogram, Subject name: Physiology
[{'content': 'Atrial depolarization in ECG is represented by \nSelect and explain. \nA. 1, B. 2, C. 3, D. 4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 1 (Description: P wave in EC6)', 'role': 'assistant'}]