Q: Where are roundworms useful in an ecosystem?
Options:
- (A) killing animals
- (B) soils
- (C) fields
- (D) bacteria
- (E) eating plants
- (F) wetland
- (G) food
- (H) alveoli
Let's think step by step below.

user
Roundworms make up the phylum Nematoda. Also, nematoda and rotifera are important groups contributing to soils. Roundworms make important contributions to soils.
Thus, the answer is (B).
assistant