Fact 1: Avalley is formed by a river flowing.

Fact 2: Canyon formed as a consequence of river erosion.

Given the two facts above, answer the question "A valley is formed by" with the following options: 
- Sediment
 - a solute
 - calcite
 - seismic activity
 - glaciation
 - weathering
 - erosion
 - loose soil


 

       erosion  