- A river is a kind of a moving body of water
- Most canyons are formed by flowing rivers through erosion over long periods of time
- Therefore, most canyons are formed by moving body of water through erosion over long periods of time

So, most canyons are formed by moving body of water through erosion over long periods of time
Question: Natural processes shape the surface of Earth. Most canyons are formed by ___.
Context: - A river is a kind of a moving body of water 
- Most canyons are formed by flowing rivers through erosion over long periods of time