Earth is heated by the Sun. Mountains direct moist air upward. Water forms droplets when cooled. Most of Earth is covered with water.
I gave my students this multiple choice question: What is the primary cause of rainstorms?

Only one answer is correct among these 4 choices:
- Earth is heated by the Sun.
- Mountains direct moist air upward.
- Water forms droplets when cooled.
- Most of Earth is covered with water.

Could you tell me which one is correct?

Earth is heated by the Sun.