What’s Parallel to What? Parallelism and Meaning in GMATPrep


The first time I read the original sentence in the below SC problem, I thought to myself: wait, what? What are you actually trying to say?gmat parallelism I knew immediately that this would be a good one to discuss with all of you. 🙂

Let’s try it out (1 minute 15 seconds) and then we’ll dive in. This question is from the free problem set included in the new GMATPrep 2.0 version of the software.

*  Displays of the aurora borealis, or northern lights, can heat the atmosphere over the arctic enough to affect the trajectories of ballistic missiles, induce electric currents that can cause blackouts in some areas and corrosion in north-south pipelines.


(A) to affect the trajectories of ballistic missiles, induce

(B) that the trajectories of ballistic missiles are affected, induce

(C) that it affects the trajectories of ballistic missiles, induces

(D) that the trajectories of ballistic missiles are affected and induces

(E) to affect the trajectories of ballistic missiles and induce


This was my thought process as I read that first sentence:



Displays of the aurora borealis, or northern lights, can heat Core sentence: displays can heat
the atmosphere over the arctic enough to affect underline just started; why here?
the trajectories of ballistic missiles, induce Ah, parallelism! It’s a list. To affect, (to) induce so I’m looking for an and followed by a third infinitive verb.
electric currents that can cause blackouts in some areas and Great, here’s the and
corrosion in north-south pipelines Huh? Okay, corrosion clearly doesn’t fit with the first two “ it’s not an infinitive verb
Now I’m confused about the basic meaning. The northern lights affect missile trajectories, induce currents and cause corrosion? Is that what they’re trying to say but they didn’t put the verb in? Something seems weird. The first two are verbs “ and we do need a verb to follow heat the atmosphere enough to do something else but the third one is a noun and I can’t change it. It’s not underlined.


Right about now, I noticed something that changed my entire view of the sentence. Initially, after seeing what looked like the first two items on a list, my instinct was to look for a list of three things: X, Y, and Z. By the end, though, I’m questioning my instinct because it seems like I have to have verb forms and yet that third item, a noun, can’t be changed (since it isn’t underlined). What to do?

And this is when I notice a tiny little detail that opened up the problem for me. The structure for a list of three things is X, Y, and Z. We have to have a comma after the Y and before the and. But there’s no comma before the and in the original sentence! In other words that and corrosion piece is not intended to be the third item in a list of three things!

Wow. Okay, if that and is not meant to be the third item in the list, then what does it go with? The word and always indicates parallelism, so what is corrosion parallel to?

Oh, I think I get it now. Check this out:

electric currents that can cause blackouts in some areas and corrosion in north-south pipelines.

The structure is actually cause X and Y where X = blackouts and Y = corrosion.

Where does that leave us with the earlier part of the sentence? I’m not sure. Maybe the first two things need an and in order to make them parallel (affect and induce). Or maybe the second item is supposed to be a modifier for the first, something like this: affect the trajectories of missiles, inducing electric currents that can cause X and Y. I have no idea how they’ll try to fix this “ time to check the other answers (and eliminate answer A)!

answer text

does it fix the problem?

(B) that (X) the trajectories, (Y) induce No. Trajectories is a noun, but induce is a verb; they’re not parallel. Eliminate B.
(C) that it (X) affects, (Y) induces and? No. Affects and induces are parallel but they have no and in between. We still can’t use and corrosion as the third item on the list, though, both because there’s no comma before the word and and because corrosion is a noun while affects and induces are verbs. Eliminate C.
(D) that the trajectories (X) are affected and (Y) induces No. They inserted the word and between the two verbs, which is a good move, but are affected is plural (and matches the plural subject trajectories), while induces is singular (and so doesn’t match the plural subject). Eliminate D.
(E) to (X) affect and (Y) induce Bingo! They’ve inserted the word and between the two verbs and also made sure that the two are parallel (they’re both in the infinitive form).


The correct answer is E.

The core structure of the correct sentence (E) is:

Displays (of the aurora borealis) can heat the atmosphere enough to affect X and induce Y.

That Y portion can be broken out in this way:

electric currents that can cause M and N

Note that the problem also tests a particular idiom: can heat X enough to Y. Answers B, C, and D all incorrectly replace the word to with the word that: can heat X enough that Y.

Be very careful when learning this idiom; in other circumstances, the word enough can be followed by the word that. This sentence is correct, for example: Studying is important enough that we should make it a priority. In our given sentence, though, we were trying to say that the atmosphere could be heated enough to cause another action to happen. The action should be in verb form: enough to .


Key Takeaways for Parallelism and Meaning

(1) Sometimes, the original sentence will seem to imply a certain structure or a certain way of reading it only to fall apart as you continue to read the sentence. This might also mess up your understanding of the meaning of the sentence.

(2) If this happens, try to figure out why you had a certain expectation in the first place. I thought the sentence was going to have the X, Y, and Z structure, because the first two components (X, Y) were there. Once I looked for the third element (, and Z) and realized that the sentence couldn’t work that way, I was on my way to solving the problem.

(3) Little clues can sometimes make a big difference. In the real world, you will see lists written in two different ways: X, Y and Z or X, Y, and Z. What’s the difference? The presence or absence of the second comma. The GMAT always uses the second comma (the latter example), so if you think you might have a list of three things but something seems funny, look for that comma. If it’s not there, then that sentence or answer choice is not trying to give a list of three things.

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

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  3. Sophie February 28, 2013 at 4:45 am

    Thanks! Very insightful. Here are my thoughts

    When Fashion meet with GMAT unexpectedly

    Introduction (How I become interested in fashion)
    When I was young, I mean when I was in Elementary School, I began to wear jeans, and I was completely fascinated in wearing them. I remembered that I wore them when I was alone at home, and I use heavy strength to tighten them on my thigh and buttocks. After putting them on, I wear my favorite belt to make them even tighter. Then I went to spray a kind of perfume called Nina which I got from my boyfriend on my bottom. And I not only feel comfortable but also meet my demanding of being pretty. They completely showed my curve. Filled with happiness, I sat on the leather seat for the whole afternoon and read fashion magazine. And feel a bit of hot because it was summer afternoon. I was forced to go to take a math class in 4pm in the afternoon. So I think I should take them off because I was a low-key at that time. So I changed a pair of loosen pants without any smell and then went to class. The teacher was an old man whose clothes smell so bad that I almost let out. At that time, I was regret to wear that pair of jeans. But, tomorrow I would wear no matter what. When the days came, I wore them to the teacher’s house to have class. The boys and teacher all feel good after smell that kind of perfume. And from that day, I can see more smile on people’s face. At that night, I was so glad that I persuaded myself to wear them when I slept. And I always imagine that picture on my mind even when I had dinner with my parents. My parents all think I was weird that night. They were right. When they went to sleep, I opened my wardrobe to find my G-string and agent provocateur. Then Input them on and spray perfume on them. After forced them to be tightly wrapped on my skin, I got into my bed. And I open iPod Nano to play “Turn It Up” which sang by Paris Hilton. And I was completely lost in the rhythm, feeling great…

    It seems that I got addicted in doing this. Every night I cannot control myself to not think that, but I know it can make me feel right. And I almost did it every week.

    I was completely indulge myself into making myself more fashion than before, and I was complemented by my headmaster and classmates around me, what’s more, I got the first place in winning the trousers designing competition which held by S.U.

    At that day, I can told you how inspired I was: First, I just felt that the other student was so conservative that they didn’t have a way to make the trousers more tempting that can make people tower them. And only fashion make do this. Fashion indeed plays an important role in designing stuffs. What I did with that pair of trousers was to use scissors to cut some cracks and holes. And then used ink pen to paint on the part which I had modified before. The crotch of the trousers is very easy to be ignore by designer, so what I do was cut it out the original material, and then put a tiny piece of lace on the cut part. And it perfectly matched each other. When I went to shop to watch girl’s clothes, I always saw detail on their clothes. And because girls are very careful. So I think maybe this is the reason why girls’ clothes are attractive.

    When I was free I often went to book shop to read books about color, clothes matching etc. Although, I didn’t choose Fashion designing as my major, I believe if I kept moving on, I will be successful in the future. The only thing I need to do is not give up.
    Honestly, I really didn’t know why I have this idea and why I was so interested in clothes designing. I think maybe there is some talents in my DNA. When I tried to put on skinny jeans 10 years ago, I began to find that I really like them, from the bottom of my heart. I feel them completely by my heart and soul.

    When I was in middle school, I started tower jeans when I went to bed. I mean I wore them when I was sleeping. And when woke up in the morning, I threw back the covers, and then I realized that I had not undressed. The smell of Nina came from the inside of coverlet. That was really great.

    At the first sight of a girl’s a pair of jeans. I became obsessed with them. The designing. The detail. How it can highlight a girl’s curve. These are the things that came from my mind.

    At home, I kept drawing clothes like jeans, Tee, hot pants etc. My mother said to me: Wow, how beautiful, are you going to be a clothes designer?

    Sadly, being a clothes designer cannot get more money or treat than being an accountant, an investor or a financial manager.

    So I have to study in B school in the future…

    However, I still can study designing by myself. Here I use my heart and soul to write this project which is called when meet with GMAT fashion unexpectedly. Again I want to mention that I was fascinated by fashion, designing, clothing matching since my childhood. Ideally want to go to college like art and designing school for further learning, but due to the condition in which I cannot get a better job. The only college for me is just like b-school, so I embark on taking GMAT. However, can combine what I like into GMAT, the answer is yes. I always believe. Then I begin this project. What I want is combine them together and look the GMAT at totally different point of view. As I have found GMAT is a kind of beauty.

    Making sense (How I combine them together)
    So let the story began:

    There are basically three parts in Verbal: Sentence Correction, Critical Reasoning and Reading Comprehensions.

    Let’s start from the RC first, which I think is the most important part of three. So what is your problem in RC? I found as for me, I completely don’t know what to do when a long passage in front of me. There are a lot of information, a complex information. We need to get its idea.

    I found that there are a lot of modifier in the passage.

    Modifier is similar to accessories, especially like necklace on your neck, the rivet on your skinny jeans.

    From the angle of beauty, modifier can always create a clear, bright and rich of layering on human’s vision and psychological sense.

    Nowadays, we have been deeply influenced by what the other people wear, and by what we recognize is great. For example:Jeans can match almost all of the clothes like tee, shirt, etc.

    Generally, wear a lot at the top, but wear only a little at the bottom (sometime it is tight, like skinny jeans or hot pants). So, what is the point, why do they wear like that? Have you ever ask yourself about such kind of questions: why just wear casually, I mean whatever they want, I think the key is they want to create a vision effect.

    There is no such a perfect thing in the world. So do the clothes. The important thing is not the dress itself, but is the overall effect.

    Learn to match color, it can save money. For example, the clothes in your closet, you can only be measured out ten, learned to color matching, suddenly discovered that there are many colors can mix with each other, the same amount of clothes, you will get 20 ways to match.