The mass of a planet causes the pull of gravity on that planet, and mass, the amount of matter in an object, is measured in grams. Given these facts, what part of a planet causes the pull of gravity on that planet among the following options:
- solid, liquid, gas
 - layers of fat
 - barrel-shaped
 - our star
 - amount of matter
 - an external framework
 - hydrogen and oxygen
 - It expands


 

     amount of matter    