Source: Official Guide for the GMAT 13th Ed. Sentence Correction; #106 Official Guide for the GMAT 2015 14th Ed. Sentence Correction; #106


Originally developed for detecting air pollutants, a

Originally developed for detecting air pollutants, a technique called proton-induced X-ray emission, which can quickly analyze the chemical elements in almost any substance without destroying it, is finding uses in medicine, archaeology, and criminology.

3 Explanations


Billy Yuan

In the first modifier of answer choice (A), isn't the antecedent of "it" unclear? (In the video, the "it" portion of the sentence wasn't written out). Logically, "it" refers to the substance, but couldn't "it" also refer to the technique? Choice (E) refers to "it" as the substance and avoids ambiguity, but it does sound repetitive and awkward. Thanks!

Aug 11, 2015 • Comment

Sam Kinsman, Magoosh Tutor

Hi Billy, pronouns usually refer to the closest noun that they agree with (in number and gender). In this sentence, "substance" is right before the pronoun "it," and is much closer than "a technique," so it's clear that the antecedent of "it" is "substance."
Also keep in mind that "it" is not in the first modifier of the sentence - the first modifier is "originally developed for detecting air pollutants"!

Oct 1, 2015 • Reply


Meishan Lin

answer choice A, doesn't "which" modify "emission"? but "which can quickly analyze the" should modify "a technique", right?

Jul 19, 2015 • Comment

Jonathan , Magoosh Tutor

Hi Meishan,
In this case, "proton-induced X-ray emission" IS referring to the "technique;" it is the name of the technique, so "which" can be said to refer to either.

"proton-induced X-ray emission" is the full noun , so we wouldn't say that "which" modifies "emission" only.

Note that there are exceptions to the "touch rule," which Mike discusses in the Magoosh lesson "Exceptions to the Touch Rule" as well as in this blog post:

I hope that helps! :)

Jul 27, 2015 • Reply


Gravatar Mike McGarry, Magoosh Tutor

May 23, 2013 • Comment

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