Contact between rocks over long periods of time causes rocks to smooth, and smoothed, grooved and polished rocks are produced by glacial erosion. Given these facts, what is erosion among the following options:
- moonlight
 - looseness of dirt or compost
 - permineralization
 - water vapor
 - fog
 - The area was once underwater
 - fissures of hot, acidic water
 - contact between rocks


 

        contact between rocks 