This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
PR interval corresponds to ECG changes as 
Select and explain. 
A. Ventricular depolarization, B. Ventricular depolarization and atrial rcpolarization, C. Atrial depolarization and conduction through AV node, D. Ventricular repolarization
C: Atrial depolarization and conduction through AV node
Answer: C: Atrial depolarization and conduction through AV node 
Explanation: C. i.e. (Atrial - depolarization and conduction through AV node) (551 - Ganong 22nd) (494- Ganong 23rd)ECG IntervalsIntervalNormal Durations (S)Events in the heart during intervalAverageRangePR interval0.180.12-0.20**Atrial depolarization and conduction through AV nodeQRS duration0.08to 0.10Ventricular depolarization and atrial repolarizationQT interval0.40to 0.43Ventricular depolarization plus ventricular repolarizationST interval (QT minus QRS)0.32 Ventricular repolarization* QRS complex denotes - ventricular depolarization*** The normal direction of mean QRS vector is generally said to be - 30 to + 110 on the coordinate system*** U wave - It is due to slow repolarization of papillary muscle* TP segment - It represents polarized state of whole heart* J-point - point between 'S' wave and ST segment. It is a point of "no" electrical activity (305-A.K Jain 3rd)