You are presented with the question "What are canyons formed by?" and the following answer choices: 
- clouds
 - stars
 - erosion
 - loose soil
 - wind
 - ice wedging
 - rainwater
 - calcite

Now knowing that most canyons are formed by flowing rivers through erosion over long periods of time and rivers, rainwater, well water and most lakes contain fresh water, choose the best answer.


 

       rainwater  