You are presented with the question "What forms soil?" and the following answer choices: 
- Earthworms
 - single-celled organisms
 - an external framework
 - space travel
 - most organisms
 - sandstone eroding
 - water freezing
 - ice forming

Now knowing that soil is formed by rocks eroding and examples of such rock include sandstone and shale , choose the best answer.


 

      sandstone eroding   