A. The normal P-R interval ranges from 0.12 to 0.20 seconds. A P-R interval longer than 0.20 seconds is considered prolonged and may indicate a first-degree AV block. B. The T wave represents ventricular repolarization. Normally, the T wave is upright in most leads. An inverted T wave can indicate various conditions, including ischemia, electrolyte imbalances, or other abnormalities C. The normal QRS duration ranges from 0.06 to 0.10 seconds. A QRS duration greater than 0.10 seconds indicates a delay in ventricular conduction, which could be due to a bundle branch block or other conduction abnormalities. D. In a normal sinus rhythm, the P wave should consistently appear before each QRS complex. This reflects proper atrial depolarization followed by ventricular depolarization. This pattern indicates that the heart's electrical impulses are originating from the sinus node and are being properly conducted through the AV node to the ventricles.