Why Is the Electrical Signal Delayed Slightly at the AV

Why is the electrical signal delayed slightly at the AV node?
1) To allow better filling of the ventricles
2) To protect the ventricles against excessively rapid atrial rates
3) To provide time for atrial contraction prior to ventricular systole
4) To prevent premature atrial beats from reaching the ventricles

A) 1 and 3
B) 2 and4
C) 1 and 2
D) 2, 3, and 4