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

Fact 2: Rivers contain 0.001 percent of the earth's water.

Given the two facts above, answer the question "What are most canyons caused by?" with the following options: 
- erosion
 - Physical weathering
 - magic
 - Freezing temperature
 - Flowing water
 - ice wedging
 - Flowing gas
 - flooding


 

     Flowing water    