Fact 1: Soil is formed by rocks eroding.

Fact 2: Rivers erode the rocks they flow over.

Given the two facts above, answer the question "What forms soil?" with the following options: 
- one celled organisms
 - single-celled organisms
 - an external framework
 - erosion from rivers
 - Earthworms
 - Sand dollars
 - The area was once underwater
 - most organisms


 

    erosion from rivers     