Hippopotamuses allow their hides and teeth to be cleaned by carp

Hippopotamuses allow their hides and teeth to be cleaned by carp, members of the genus labeo, which, in turn, benefit by eating the algae and parasites on the giant mammals.

(A) which, in turn, benefit by eating the algae and parasites on the giant mammals

which, properly refers to to subjuct + Proper use of "in turn" + Subject-Verb Agreement.

(B) which benefits by eating the algae and parasites on the giant mammals in turn

Subject-Verb Agreement, carp is plural as specified by the use of "Members of the genus labeo"

(C) benefiting, in turn, by eating the algae and parasites on the giant mammals

Allow + Cleaned =/= benefiting + eating Not Parallel

(D) to benefit, in turn, by eating the algae and parasites on the giant animals

"to benefit" in ungrammatical and skews the meaning

(E) who benefits by eating the algae and parasites on the giant mammals in turn

Subject-Verb Agreement, carp is plural as specified by the use of "Members of the genus labeo"

(A) which, in turn, benefit by eating the algae and parasites on the giant mammals

Looks good.

(B) which benefits by eating the algae and parasites on the giant mammals in turn

1) SVA error. By saying "Benefits", we could interpret this as referring to a specific carp, which changes the meaning.
2) "In turn" at the end doesn't make much sense

(C) benefiting, in turn, by eating the algae and parasites on the giant mammals

Incomplete sentence

(D) to benefit, in turn, by eating the algae and parasites on the giant animals

Sentence just doesn't make sense..

(E) who benefits by eating the algae and parasites on the giant mammals in turn

"Who" can only modify humans.. Not animals
"In turn" should be earlier in the sentence, this sort of composition doesn't make sense.

Hippopotamuses allow their hides and teeth to be cleaned by carp, members of the genus labeo, which, in turn, benefit by eating the algae and parasites on the giant mammals.
(A) which, in turn, benefit by eating the algae and parasites on the giant mammals - Correct - correctly modifies carp
(B) which benefits by eating the algae and parasites on the giant mammals in turn - Incorrect - placement of 'in turn' is awkward
(C) benefiting, in turn, by eating the algae and parasites on the giant mammals - Incorrect - this incorrect modifies Hippos and distorts meaning - carps are benefiting but this sentence states that Hippos are benefiting
(D) to benefit, in turn, by eating the algae and parasites on the giant animals - Incorrect - to benefit is incorrect - it is not clear who is benefiting
(E) who benefits by eating the algae and parasites on the giant mammals in turn - Incorrect - Not clear what "who" refers to - whether carps or hippos?

Shouldn't it be 'benefits' as carp is singular?

Posted from my mobile device

Hippopotamuses allow their hides and teeth to be cleaned by carp, members of the genus labeo, which, in turn, benefit by eating the algae and parasites on the giant mammals.

(A) which, in turn, benefit by eating the algae and parasites on the giant mammals
which refers to the members so plural benefit is correct.

(B) which benefits by eating the algae and parasites on the giant mammals in turn
which refers to the members so verb should be plural and not singular benefits. Incorrect

(C) benefiting, in turn, by eating the algae and parasites on the giant mammals
benefitting is v+ing modifier which modifies the previous clause which is incorrect in this context. Incorrect.

(D) to benefit, in turn, by eating the algae and parasites on the giant animals
to is incorrect here. It is an incomplete sentence.

(E) who benefits by eating the algae and parasites on the giant mammals in turn
who is used for people and not animals or anything else. Incorrect.

Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.