Why Does an Occluded Front Form

Multiple Choice

Why does an occluded front form?

A) Slow moving cold fronts push warm fronts downward.
B) Slow moving cold fronts are overtaken by warm fronts.
C) Fast moving cold fronts overtake other cold fronts.
D) Fast moving cold fronts push warm air downward.
E) Fast moving cold fronts overtake warm fronts and keeps it aloft.