You are presented with the question "_ contribute to soils." and the following answer choices: 
- Sediment
 - Aphids
 - cacti
 - Roundworms
 - Exfoliation
 - Amphibians
 - Ringworms
 - rainfall

Now knowing that roundworms make up the phylum Nematoda and also, nematoda and rotifera are important groups contributing to soils, choose the best answer.


 

    Roundworms     