Nutritionists agree that elevated cholesterol levels contribute to

Ok, but all these points support the idea that B would actually work (The parallelism point doesn't make sense as it follows the same format as the OA).

Them is the object "cholesterol levels" and cannot be any other object due to plurality. So why is B incorrect?

Option B has a severe pronoun error. In a sentence all they /their/ them must refer to the same antecedent. In option B, "they" and "them" have different antecedents.

So you're saying if i use they in the same sentence as them they both have to refer to the same antecedent? This is really confusing, because "they" is usually the subject and "them" is usually the object of the clause. How can the subject and object logically be referred to the same instance? Could you provide examples? Because this is the first time I've heard this rule.

Yes, absolutely - you have understood right - this is a strictly followed rule in GMAT. Any good GMAT guide ( e.g. Manhattan SC guide) highlights this rule. If you have completed an SC guide and have not come across this rule, then I would say that you will have to read a guide again, this time a good one.

The subject and object may NOT be in the same clause, i.e. for the same verb. (If they are for the same clause "themselves" instead of "them" must be used.) Following is an example from Manhattan SC guide:

Researchers claim to have developed new "nano-papers" incorporating tiny cellulose fibers, which THEY allege give THEM the strength of cast iron.

What nouns do they and them refer to? You might assume that they refers to researchers (who claim something) and that them refers to new “nano-papers? However, this confusing switch of reference is not permitted by the GMAT.

That makes sense thank you Sayan!

Official Explanation:

This sentence is correct as written.

The underlined portion of the sentence contains the third-person pronoun they, so check whether the pronoun agrees in number with its referent. The plural they clearly refers to nutritionists. There appear to be no errors in the original sentence, so keep choice A. Because there are no errors in the original sentence, there are no obvious repeaters to look for. Evaluate the remaining choices individually, looking for reasons to eliminate each answer.

Choice B introduces a pronoun error by replacing the phrase these elevated levels with the pronoun them. These elevated levels clearly refers to cholesterol levels, but there are two plural nouns in the sentence to which the pronoun them might refer. Since the referent of the pronoun them is ambiguous, eliminate choice B. Choice C repeats the pronoun error introduced in choice B, replacing these elevated levels with the pronoun them. In addition, choice C introduces an idiom error by replacing not with neither. The word neither forms the first part of a correlative conjunction, neither…nor. Choice C pairs neither with or, which is not idiomatic. Eliminate choice C. Choice D creates a new error by employing the pronoun their, the referent of which is ambiguous. In addition, choice D creates a parallel construction error by introducing a list the elements of which represent different parts of speech. The first item, determined, is a verb, but the second item, how, is an adverb. Eliminate choice D. Choice E creates a subject-verb agreement error by introducing the clause levels is. In addition, the referent of the pronoun their is ambiguous. Eliminate choice E.

Choice A: Correct.

Choice B: No. The referent of the pronoun them is ambiguous. Pronoun ambiguity.

Choice C: No. The referent of the pronoun them is ambiguous, and the correct idiom is neither…nor. Pronoun ambiguity; Idiom.

Choice D: No. The referent of the pronoun their is ambiguous, and the items in the list, determined… and how…, do not represent the same part of speech. Pronoun ambiguity; Parallel construction.

Choice E: No. The singular verb is does not agree in number with the plural subject levels, and the referent of the pronoun their is ambiguous. Subject-Verb agreement; Pronoun ambiguity.

The correct answer is choice A.

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