Dealing With Partial Underlines in Sentence Correction

by , Jul 16, 2011

It has been a while since weve done grammar, so lets 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 wasnt 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, dont 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, lets 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. Thats important because the non-underlined part is set in stone I cant 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. Ive shown the first two methods in previous articles (for other problems), so lets 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. Thats 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 thats 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? :) )

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 cant 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; well 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.

Lets see. Weve 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 wheres the by? Oh, right, its part of the X. Cant 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 cant reuse it for the Y. The Y does include the word by, but its missing the word accompanied, leaving us with (for the Y):

the increase is by an increase in volume

Eliminate C. Moving on to D. Theyve 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 cant reuse it for Y, and the Y includes only by without the accompanied. Eliminate D.

Finally, were 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! Weve 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.

Es the answer; its 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 wasnt 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 isnt in the sentence. We have the verb increased. But a pronoun cant refer to a verb; its supposed to refer to a noun. So thats 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, its referring to gas, but theres also an expectation that, if we use it twice in the same sentence, well 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 its 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 cant 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.