The Main Reason That Polar Regions Are Cooler Than the Equator

The main reason that polar regions are cooler than the equator is that

A) there is more ice at polar regions.
B) sunlight strikes polar regions at a lower angle.
C) the polar regions are farther from the sun.
D) the polar regions' atmosphere is thinner and contains fewer greenhouse gases.
E) the polar regions are permanently tilted away from the sun.