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
Atrial depolarization in ECG is represented by 
Select and explain. 
A. 1, B. 2, C. 3, D. 4
A: 1
Answer: A: 1 
Explanation: 1 (Description: P wave in EC6)