Final answer:
The QT interval on an ECG is measured from the beginning of the QRS complex to the end of the T wave, representing the period of ventricular electrical and mechanical activity.
Step-by-step explanation:
The QT interval on an electrocardiogram (ECG) is measured from the beginning of the QRS complex to the end of the T wave. correctly describes where to measure the QT interval. The QT interval represents the total time it takes for the ventricles to depolarize and then repolarize, which corresponds to the period of ventricular activity both electrically and mechanically