You are presented with the question "What forms soil?" and the following answer choices: 
- one celled organisms
 - single-celled organisms
 - an external framework
 - erosion from rivers
 - Earthworms
 - Sand dollars
 - The area was once underwater
 - most organisms

Now knowing that soil is formed by rocks eroding and rivers erode the rocks they flow over, choose the best answer.


 

    erosion from rivers     