In an Electrocardiogram EKG tracing the P wave represents?

A. Ventricular repolarization is represented by the T wave on an EKG. B. Left arterial pressure is not represented by any specific EKG waveform. C. Ventricular depolarization is represented by the QRS complex on an EKG. D. The P wave represents atrial depolarization, which is the electrical activity that initiates atrial contraction.