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 "Wave action causes?" with the following options: 
- fissures of hot, acidic water
 - contact between rocks
 - Animal survival
 - Electrical energy
 - scattered light
 - flow of electrons
 - electromagnetic energy
 - energy of moving objects


 

  contact between rocks       