You are presented with the question "what are most canyons formed by over long periods of time?" and the following answer choices: 
- hurricanes
 - wind tunnels
 - dangerous
 - forces
 - kalenchoes
 - flooding
 - high populations
 - Sediment

Now knowing that most canyons are formed by flowing rivers through erosion over long periods of time and most river erosion occurs when the river is in flood, choose the best answer.


 

      flooding   