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

Fact 2: Rocks on the streambed are subrounded and fairly smooth.

Given the two facts above, answer the question "Contact between rocks over long periods of time causes rocks to be what?" with the following options: 
- coiled
 - homogenous
 - inactive
 - subrounded
 - dormant state
 - barrel-shaped
 - erosion
 - threatened


 

    subrounded     