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

Fact 2: Granite is a common rock in continents.

Given the two facts above, answer the question "what smooths over long periods of time due to contact?" with the following options: 
- h2o
 - alluvial
 - granite
 - calcite
 - loose soil
 - soil
 - mountains
 - erosion


 

   granite      