From a functional point of view, which pair of interactions is equivalent?

Question

A. Cleaner and client fish, and ants and aphids.
B. Cleaner and client fish, and ants and acacias.
C. Ants and aphids, and ants and acacias.
D. Ants and acacias, and humans and cattle.

*NOTE: I just want to know what this question really means and how can I figure out how to approach the answer. I don't really understand what this question is asking... I mean, all of these answers provided, aren't their interactions equivalent??