You are presented with the question "Where are roundworms useful in an ecosystem?" and the following answer choices: 
- killing animals
 - soils
 - fields
 - bacteria
 - eating plants
 - wetland
 - food
 - alveoli

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


 

  soils       