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

Fact 2: Because of the big wave action, the rocks are very smooth.

Given the two facts above, answer the question "What causes contact between rocks?" with the following options: 
- wind
 - heat
 - erosion
 - deltas
 - waves
 - motion
 - seasons
 - rivers


 

     waves    