Commensalism is any relationship between two living things in which on

E, the argument gives us a definition of commensalism (although not a word ) and then gives us a example of Oxpecker birds as commensal species that feed on ticks that are attracted to large mammal's fur. It wants us to infer the roles played by ticks, oxpecker birds and the mammals.

Commensalism is any relationship between two living things in which one benefits and the other is
neither helped nor harmed. Oxpecker birds are commensal species that flock with the large mammals
of the African Savannah. They feed on ticks, fleas, and flies that are attracted to the mammals' fur.

Which of the following, if true, can most reasonably be inferred from the statements above?

(A) Oxpecker birds are neither helped nor harmed by the large mammals of the African Savannah. They do feed on the ticks, they are getting food so how are they not helped.

(B) Ticks, fleas, and flies are commensal species in their relationship with both oxpecker birds
and the large mammals of the African Savannah. They are obviously harmed (they are getting killed )

(C) No species exist in a commensal relationship with oxpecker birds except for large mammals
of the African Savannah. How can this be the inference ? It is out of scope

(D) In commensal relationships, the smaller of the species in the relationship usually benefits
while the larger is neither helped nor harmed. Does not apply to the ticks and this cannot be generalized from one example

(E) Preying on small creatures drawn to the fur of the large mammals of the African Savannah
does not significantly affect those mammals. This is correct because one would think that when oxpecker birds are feeding on ticks they are getting the benefit, but due to the birds' eating of ticks, large mammals might also be getting the benefit, so relationship is not clear. The inference says that the large mammals are not significantly affected, Hence the clear relationship is established.