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GMAT Tips – Dealing With Partial Underlines in Sentence Correction

Today’s GMAT tip comes from test prep firm ManhattanGMAT. In this article, they provide helpful tips for how to answer sentence correction questions involving partial underlines on the GMAT.  Read on to see what they have to say!

It has been a while since we’ve done grammar, so let’s try out this GMATPrep Sentence Correction question. Set your timer for 1 minute and 15 seconds and go!

When the temperature of a gas is increased, it is either accompanied by an increase in pressure if the gas is enclosed in a container, or an increase in volume if the gas is able to expand.

“(A) When the temperature of a gas is increased, it is either accompanied by an increase in pressure if the gas is enclosed in a container, or

“(B) When the temperature of a gas is increased, it is accompanied either by an increase in pressure if it is enclosed in a container or

“(C) When the temperature of a gas is increased, the increase is either accompanied by an increase in pressure if the gas is enclosed in a container or by

“(D) Any increase in the temperature of a gas is either accompanied by an increase in pressure if it is enclosed in a container, or by

“(E) Any increase in the temperature of a gas is accompanied either by an increase in pressure if the gas is enclosed in a container or by”

[Note to those who answered the problem within the allotted time frame and thought it wasn’t too hard. Did you read the answer choices horizontally? Or did you compare choices vertically? You may be able to get away with a horizontal strategy for this problem, but if you want to get better, then you need to learn the vertical strategy for harder problems. If this problem was easier for you, don’t dismiss it. Use it to learn how to tackle harder problems. (And use this principle in general: easier problems are VERY good for learning how to tackle harder problems.)]

Okay, have you got your answer? Now, let’s dive into this thing! What did you think when you read the original sentence?

The first thing I noticed was that only part of the sentence is underlined. That’s important because the non-underlined part is “set in stone” – I can’t change it. I have to make the underlined part match the non-underlined part.

I have a few options for my approach here. I can read the original sentence and see whether I find any errors. I can try to “strip” the original sentence down to its core components. Or I can try to figure out how the non-underlined part fits into the overall sentence structure. I’ve shown the first two methods in previous articles (for other problems), so let’s try that third method in this article.

The non-underlined portion reads:

“an increase in volume if the gas is able to expand”

Leading into that, in the original sentence, is the word “or.” That’s interesting. The word “or” is a parallelism marker, so apparently parallelism might be an issue here. I glance through the end of each answer choice and notice that “or” is there every time (sometimes followed by the word “by”). Okay, so parallelism is definitely an issue, and that’s really important to know because I have to make that non-underlined stuff parallel to something else… something that is part of the underline.

My first task is to figure out the other half that goes along with the non-underlined portion. In this problem, they give us another great clue: the word “either.” “Either X or Y” is an idiom; the X and the Y need to be written in the same structural form. Further, I should be able to take the part before the idiom starts (before the “either”) and finish the sentence with either the X or the Y. (See what I just did there? J)

What do we have for this parallel structure in the original sentence?

either accompanied by an increase in pressure if the gas is enclosed in a container, or an increase in volume if the gas is able to expand.”

Okay, so the X follows “either” and the Y follows “or.” Are the X and Y parallel?

No. X begins “accompanied by an increase” while Y begins simply with “an increase.” Further, if we try to construct the sentence only with the X and then only with the Y, we get:

“it is accompanied by an increase in pressure if the gas is enclosed in a container.”

“it is an increase in volume if the gas is able to expand.”

The first sentence (with the X) is fine. (Note that you drop the idiom marker, “either,” when using this technique.) The second sentence, however, is not fine. We want to say that it is accompanied by an increase in volume, not that it just is an increase in volume. The “accompanied by,” however, is part of the X, so we can’t reuse it for the Y. Whatever is after the “either” can only be used for X and whatever is after the “or” can only be used for Y.

We can eliminate answer A and then we want to try to reuse that same reasoning to eliminate any other answers (if possible). We already know that we have the “or” parallelism marker in every answer choice. We may or may not have the “either” marker; we’ll have to check as we go along.

Answer B says (in part):

“it is accompanied either by an increase in pressure if it is enclosed in a container or an increase in volume if the gas is able to expand.”

Let’s see. We’ve got the “either” marker again. X = “by an increase” and Y = “an increase.” Not parallel! Look what happens to the full sentence when we try to use Y individually:

“it is accompanied an increase in volume…”

It should say “by an increase in volume” – where’s the by? Oh, right, it’s part of the X. Can’t use it for the Y. Eliminate B.

Answer C says (in part):

“the increase is either accompanied by an increase in pressure if the gas is enclosed in a container or by an increase in volume if the gas is able to expand.”

The “either” marker is there again. This one pretty much repeats the problem in A; “accompanied by” is part of the X, so we can’t reuse it for the Y. The Y does include the word “by,” but it’s missing the word “accompanied,” leaving us with (for the Y):

“the increase is by an increase in volume…”

Eliminate C. Moving on to D. They’ve switched up the beginning of the sentence, but we still have that “either” in D:

“Any increase in the temperature of a gas is either accompanied by an increase in pressure if it is enclosed in a container, or by

Once again, the “accompanied by” is part of X, so we can’t reuse it for Y, and the Y includes only “by” without the “accompanied.” Eliminate D.

Finally, we’re down to E. I hope it works!

“Any increase in the temperature of a gas is accompanied either by an increase in pressure if the gas is enclosed in a container or by”

Lets’ see. X = by an increase in pressure. Y = by an increase in volume. Bingo! We’ve got parallelism here. Notice that it works with the full sentence as well:

X: “Any increase… is accompanied by an increase in pressure.”

Y: “Any increase… is accompanied by an increase in volume.”

E’s the answer; it’s the only one that makes X and Y parallel.

We got a bit lucky on this one; we were able to eliminate all four wrong answers based upon the same issue. But it wasn’t completely just luck that started us down this path – it was noticing specifically where the underline started and what implications that had for matching the non-underlined portion to the underlined portion. The clues are there; part of your task as a student is to learn how to read them!

There are other reasons we can use to eliminate some wrong answers. For example, A and B both begin:

“When the temperature of a gas is increased, it is (accompanied by an increase in pressure…)”

What is the antecedent for the pronoun “it”? (“Antecedent” is the official grammar term for “the noun that the pronoun is talking about.”)

Temperature? The temperature is accompanied by an increase in pressure? No, not just the temperature. The increase in temperature also causes an increase in pressure. So the pronoun “it” is referring to the noun “increase.”

Er. Except the noun “increase” isn’t in the sentence. We have the verb “increased.” But a pronoun can’t refer to a verb; it’s supposed to refer to a noun. So that’s no good; eliminate A and B. And note that B has another “it” later on; that “it” is ambiguous. Is it referring to gas or to temperature? Logically, it’s referring to “gas,” but there’s also an expectation that, if we use “it” twice in the same sentence, we’ll be referring to the same thing each time… and that first “it” is not referring to gas.

Answer C resolves the “it” issue by replacing the pronoun with the words “the increase.” This is the correct meaning, but it’s a bit clunky. And, of course, that parallelism error exists later in choice C.

So, there are multiple ways to get there, but all (correct!) paths lead to the same end: the correct answer is E.

Key Takeaways for Partial-Underline Sentences on SC:

(1) Partially underlined sentences contain, by definition, some portion of a sentence that can’t change and therefore must be correct. Ask yourself how that non-underlined portion connects to the rest of the sentence. What clues exist to help tell you what that connection is or might be?

(2) When parallelism is required, the “X” and “Y” portions must be both structurally and logically parallel. The part of speech of the main word should be the same for both, and the full sentence should be able to be written with just the X or just the Y and still be grammatically correct.

* GMATPrep question courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

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Posted in: GMAT - Verbal, GMAT Tips

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