Most animals can be classified as
invertebrates
arthropods
chordates
sessile

Arthropods.

Chordates and sessile animals don’t make up a whole lot of percentage of the animal kingdom, and “invertebrates” accounts for too many animals that are very different from each other so it is not a good form of classification. Arthropoda is a distinct classification of animals that have jointed limbs and a cuticle that molts. they also make up around 80% of all animals

I think the answer is D)
Hope this helps!!!:)