D because if the species was to be removed from an ecosystem, everything that needed that species as food, or the species ould have to adapt to the foods available in the new ecosystem they live in. Hope I helped, and let me know if you are still not 100% sure about the answer, and I'll try to clarify what I said.
The scheme of modern taxonomy goes:
Life > Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species
So, a PHYLUM is made of several classes.
Genetic material is found in Eukaryotic cells. Plant and animal cells both are eukaryotic cells.
