Fact 1: Contact between rocks over long periods of time causes rocks to smooth.

Fact 2: Granite is rock formed by fire.

Given the two facts above, answer the question "Contact between what over long periods of time causes them to smooth?" with the following options: 
- graptolites
 - Smooth music.
 - Contact lenses.
 - calcite
 - Granite.
 - loose soil
 - rivers
 - Time periods.


 

     Granite.    