Final answer:
On an ECG, the QRS complex represents the depolarization of the ventricles, which is the correct answer to the student's question.
Step-by-step explanation:
Ventricular depolarization in an electrocardiogram (ECG) is represented by the QRS complex. The P wave represents the depolarization of the atria, while the T wave shows the repolarization of the ventricles. During the ECG, the repolarization of the atria occurs at the same time as the QRS complex, but it is masked by the stronger electrical activity of ventricular depolarization. Therefore, for the provided options, ventricular depolarization correlates with the QRS complex.