Considered one of the most intelligent of the New World monkeys

Option A, B and C out because in non-underlined portion we have it, which calls for singular form of 'capuchins'.
Option D out because of parallelism and meaning as well.
IMO answer is option E.

Regards.,
Tamal

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Considered one of the most intelligent of the New World monkeys, capuchins cleverly create an insecticide and crush millipedes, rubbing the remains of the bugs over its back.

A) capuchins cleverly create an insecticide and crush millipedes, rubbing the remains [LOGIC]

B) capuchins cleverly create an insecticide, they crush millipedes, and with such rub the remains [comma splice = run on sentence]

C) capuchins use their cleverness to create an insecticide, crush millipedes, and rub the remains

D) the capuchin cleverly creates an insecticide , crushes millipedes, and it rubs the remains [LOGIC]

E) the capuchin cleverly creates an insecticide, crushing millipedes and rubbing the remains

EXPLANATION

• takeaway: read the non-underlined portion. In this case, its tells us that "capuchin" is singular.

• pronoun ambiguity? No. The guideline is that there can be only one logical antecedent for a pronoun. There is only one logical antecedent. See analysis beneath (A).

• Split # 1: Capuchins (plural) vs. capuchin (singular)

When we see a split such as capuchins and the capuchin, a split that is fairly common
on the GMAT, we need to find the clue in the non-underlined portion of the sentence.

Almost always in these species / animal questions, GMAC will tell us whether the noun in question is plural or singular. (I cannot recall any exception.)

This question tells us that the noun is singular, that "the capuchin" is correct.
The word ITS in the non-underlined portion of the sentence is a singular pronoun (possessive).
The pronoun is logical.
This animal needs an insecticide, which prevents bugs from biting.

Singular ITS?
Well, its cannot refer to bugs, millipedes, or remains. Those three words are plural.
Logically, its cannot refer to insecticide.
-- Insecticide is not an animal with a back.
ITS needs a singular antecedent.
ITS has one logical antecedent: the capuchin

Answers A, B, and C use the plural word capuchins, which does not agree with the singular pronoun ITS

Eliminate A, B, and C

Option A is also illogical. Sequence is off. The error is similar to that in Option D, analyzed below.

• Split #2: Parallelism

Option (D) introduces the word IT
The capuchin ... creates an insecticide, crushes millipedes, and IT rubs ...

The capuchin does three things in a list X, Y, and Z.
X, Y, and Z must be parallel. Using IT before the Z element ("it rubs") ruins the parallelism.
The word IT also can create confusion: Why do the first two verbs clearly belong with the subject capuchin whereas this third verb is attached to an IT?

The lack of parallelism is enough to eliminate D.

The logic of D is off, too. (Option A, already eliminated, has the same error.)
Creates, crushes, and rubs are not all at the same logical "level." The sequence is off.
That is, the capuchin creates an insecticide [BY crushING millipedes] and rubs the remains (the insecticide) over its own back.

Eliminate D.

I have noted other errors in the options in red typeface,
errors that if not explained here have an explanation in brackets.

The correct answer is E.

Biggest takeaway: Almost invariably, GMAC will tell us whether a noun used in this kind of question is singular or plural. Remember to look for the clue in non-underlined portions of the sentence.

COMMENTS

The answer split in this question is pretty straightforward.
If you catch ITS in the final portion of the sentence, life is a lot easier.

I laughed at this comment about B from PeepalTree : ehhh this option is a mess
True.

PeepalTree wrote an excellent answer. Best answer. Kudos!

Considered one of the most intelligent of the New World monkeys, capuchins cleverly create an insecticide and crush millipedes, rubbing the remains of the bugs over its back.

A) capuchins cleverly create an insecticide and crush millipedes, rubbing the remains --> "its" singular, "capuchins" plural

B) capuchins cleverly create an insecticide, they crush millipedes, and with such rub the remains --> same as A

C) capuchins use their cleverness to create an insecticide, crush millipedes, and rub the remains--> same as A

D) the capuchin cleverly creates an insecticide, crushes millipedes, and it rubs the remains --> not parallel

E) the capuchin cleverly creates an insecticide, crushing millipedes and rubbing the remains --> correct

A. The use of ‘and’ makes it seem like both the events are different that occur together.

B. ‘..with such’ doesn’t make sense.

C. It seems like the C use their cleverness to do three things.

D. Same as C.

E. This option properly encompasses the meaning. It says that the C creates an insecticide by crushing bugs and rubbing them over its back.

Posted from my mobile device

From the "it" in the non-underlined part, we can infer that we should use singular "capuchin", since "it" can only refer o capuchin not "one of one of the most intelligent of the New World monkeys" or anything else. Eliminate A,B,C. Remember, in GMAT, whenever you see a question with answer choices that are different in singularity, the problem will always tell you if it is singular or plural.

Comparing D and E. We see that D doesn't follow parallelism by using "it". Hence, E is correct.

This is a meaning problem:
Capuchins create insecticide by crushing millipedes and rubbing the remains of the bugs over their back. {This is the intended meaning}
A. Meaning is not clear and Capuchins and its are not in agreement.
B. Same as A
C. Same as A
D. This sentence makes the three things disjoint.
E. Correct.

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