Answer the following question: 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, _ contribute to soils.?

a). Sediment; b). Aphids; c). cacti; d). Roundworms; e). Exfoliation; f). Amphibians; g). Ringworms; h). rainfall;
Answer:
d).