Fact 1: Temperature falls from the equator to the poles.

Fact 2: All temperatures are measures of heat energy.

Given the two facts above, answer the question "what falls from the equator to the poles?" with the following options: 
- precipitation
 - heat energy
 - Greenhouse gases
 - sunlight
 - carbon dioxide
 - water vapor
 - sun's heat
 - energy


 

  heat energy       