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 "_ contribute to soils." with the following options: 
- Sediment
 - Aphids
 - cacti
 - Roundworms
 - Exfoliation
 - Amphibians
 - Ringworms
 - rainfall


 

    Roundworms     