Contact between rocks over long periods of time causes rocks to smooth.
Rocks on the streambed are subrounded and fairly smooth.
Contact between rocks over long periods of time causes rocks to be subrounded.
Contact between rocks over long periods of time causes rocks to be what?
Options:
  - coiled
  - homogenous
  - inactive
  - subrounded
  - dormant state
  - barrel-shaped
  - erosion
  - threatened