Fact 1: Gravity causes objects that have mass to be pulled down on a planet.

Fact 2: Astronomy is the scientific study of the stars, planets and the other celestial bodies.

Given the two facts above, answer the question "What causes objects to be pulled down on a celestial body?" with the following options: 
- power
 - friction
 - black hole
 - wind
 - gravity
 - orbit
 - earth
 - eclipse


 

     gravity    