Fact 1: Roundworms make up the phylum Nematoda.

Fact 2: Also, nematoda and rotifera are important groups contributing to soils.

Given the two facts above, answer the question "what contributes to soils?" with the following options: 
- roundworms
 - humans
 - rainfall
 - cacti
 - bacteria
 - weathering
 - viruses
 - Most plants


 

 roundworms        