Q: You are presented with the quiz "what falls from the equator to the poles?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "temperature falls from the equator to the poles" and "all temperatures are measures of heat energy". So, what's the best answer to the question?

Select from: 1. precipitation 2. heat energy 3. Greenhouse gases 4. sunlight 5. carbon dioxide 6. water vapor 7. sun's heat 8. energy
The answer is:
2.