Answer the following question given this paragraph: 

Gravity has traditionally been defined as a force of attraction between two masses. According to this conception of gravity, anything that has mass, no matter how small, exerts gravity on other matter. The effect of gravity is that objects exert a pull on other objects. Unlike friction, which acts only between objects that are touching, gravity also acts between objects that are not touching. In fact, gravity can act over very long distances.


Q: What has traditionally been defined as a force of attraction between two masses?

 Choices:

- motion

- mass

- volume

- gravity

A:
gravity
