Fact 1: Gravity pulls objects towards planets.

Fact 2: Because of gravitation, objects that are on or near the earth are pulled toward it.

Given the two facts above, answer the question "What causes water to stay on earth's surface?" with the following options: 
- Clouds
 - Planets
 - rainfall
 - friction
 - Gravity
 - sun's heat
 - Dirt
 - forces


 

     Gravity    