You are presented with the question "Contact between what over long periods of time causes them to smooth?" and the following answer choices: 
- graptolites
 - Smooth music.
 - Contact lenses.
 - calcite
 - Granite.
 - loose soil
 - rivers
 - Time periods.

Now knowing that contact between rocks over long periods of time causes rocks to smooth and granite is rock formed by fire, choose the best answer.


 

     Granite.    