Fact 1: Most canyons are formed by flowing rivers through erosion over long periods of time.

Fact 2: Rivers, rainwater, well water and most lakes contain fresh water.

Given the two facts above, answer the question "What are canyons formed by?" with the following options: 
- clouds
 - stars
 - erosion
 - loose soil
 - wind
 - ice wedging
 - rainwater
 - calcite


 

       rainwater  