I believe it would be the last one. "Most animals thrive where they can find food easily." Because it's telling us by which the animal finds its food.
A clause can modify verbs, adverbs, and adjectives by telling us when, where, why, how, how much and under which condition. These sentences usually begin with such, as, after, because, and although.
With a 3d answer, much like a 3d shape there is definition within the answer. What a 2d shape its just flat meaning the answer has no detail and is very plain.
