This question is from MGMAT CAT. I got this one correct but I have problem with official explanation.

Carbon monoxide levels in the atmosphere grew by enough of an increased percentage during the twentieth century that it began to trap heat radiating from the Earth, and it caused the average surface temperature to rise.
A) Carbon monoxide levels in the atmosphere grew by enough of an increased percentage during the twentieth century that it began to trap heat radiating from the Earth, and it caused the average surface temperature to rise.
B) Carbon monoxide levels in the atmosphere increased by enough of a percentage during the twentieth century that they began to trap heat radiating from the Earth, causing the average surface temperature to rise.
C) Levels of atmospheric carbon monoxide increased sufficiently during the twentieth century to begin trapping heat radiating from the Earth, causing the average surface temperature to rise.
D) Atmospheric carbon monoxide levels increased by a sufficient percentage during the twentieth century to begin trapping heat radiating from the Earth, which caused the average surface temperature to rise.
E) Levels of carbon monoxide in the atmosphere during the twentieth century increased enough to begin trapping heat radiating from the Earth, causing the average surface temperature to rise.

The official explanation says "This choice alters the position of "during the twentieth century", thereby changing the meaning of the sentence. In this choice "during the twentieth century" modifies the carbon monoxide levels instead of describing when those levels "increased." This distorts the meaning by leaving open the possibility that carbon monoxide levels "increased enough" during some other time period (e.g., the 21st century)."

How is that the "Levels of carbon monoxide in the atmosphere during the twentieth century" increased in 21st century. Isn't that in 21st century we will have "Levels of carbon monoxide in the atmosphere during the 21st century"?

What's the OA?

You posted an explanation for a choice but did not say which choice it refers to. Can you clarify?

I'm guessing you meant E, just from my read of the choices.

Here, we have "levels of carbon monoxide in the atmosphere during the 20th century" - you have the word "levels" followed by three prepositional phrases, each of which is referring to the preceding words. Ultimately, it's all talking about the levels. So there were some levels of carbon monoxide in the atmosphere during the 20th century. Let's say the level was 10, just to make it easy to talk about this.

The 20th century encompasses 1900 to 1999. The 21st century encompasses 2000 to 2099. Let's say that the "10" level was measured in 1990, which is during the 20th century.

That level, 10, then increased - but at some time not specified by the sentence. Did the level move up to 11 sometime during the rest of the 1990s? Maybe. But could the level have moved up to 11 in, say, 2001? Sure. And that would be the 21st century, not the 20th.

Essentially, in the other options, "during the 20th century" is modifying the word increase - it's telling us WHEN the increase occurred. In E, it's telling us when we are establishing the baseline level, which then increased at some time AFTER that - but the sentence doesn't say when.

Confusing I know - does that make sense?

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Stacey Koprince
Instructor
Director of Online Community
ManhattanGMAT

Great clarification. I also wanted to confirm that "Levels of atmospheric carbon monoxide" has the same meaning as "carbon monoxide levels in the atmosphere" and that the later is not "wordy". Sometimes you will see answer choices that shorten the meaning of a phrase such as this example, but are wrong because it is deemed "awkward".

If answer choice E placed "during the 20th century" correctly after the increase so that it reads "Levels of carbon monoxide in the atmosphere increased enough during the 20th century to begin...etc," would that be correct?

Thanks-

[quote="TC"]Great clarification. I also wanted to confirm that "Levels of atmospheric carbon monoxide" has the same meaning as "carbon monoxide levels in the atmosphere" and that the later is not "wordy". Sometimes you will see answer choices that shorten the meaning of a phrase such as this example, but are wrong because it is deemed "awkward".

Also, if answer choice E placed "during the 20th century" correctly after the increase so that it reads "Levels of carbon monoxide in the atmosphere increased enough during the 20th century to begin...etc," would that be correct?

Thanks-[/quote]

Hi, just checking to see if anyone is responding to my question? I posted a week ago and I am still checking back in every day...thanks!

i see problems in every answer options.
here r my thoughts -
a) Carbon monoxide levels - plural & it - singular.
b) "......they began to trap heat ......." indicates that Carbon monoxide levels have started trapping heat. i believe its not the level but the Carbon monoxide itself is trapping the heat.
c) "Levels of atmospheric carbon monoxide .................radiating from the Earth", "causing the ...................temperature to rise". two parts of the sentence r connected only by a comma. this seems to me a loose connection.
d) which - no clear antecedant.
e) same as C.


Thanks!

TC sorry for the slow reply.

Yes, your fix would make E okay. However, C would still be preferable, as "sufficiently" is better than "enough." This might not be strong enough of a split to stand alone as your final choice on a GMAT problem.

Kylo, adverbial modifiers often start with an "-ing" form after a comma. There is nothing wrong with this. In fact, this construction allows the words following the comma to correctly describe the preceding clause. Furthermore, this construction often indicates the result of the preceding clause - this is the case here.

What's the OA

The correct answer is C.


I know Jonathan already answered TC on this, but I'll throw in a quick comment. In this case, I think the meaning of "levels of atmospheric carbon monoxide" and "carbon monoxide levels in the atmosphere" are essentially identical.

However, you are wise to raise the question, because a meaning difference could be possible in a similar case. Consider the following:

"...salt concentration in the sea..." vs. "....concentration of sea salt..."

The first is clear (how much salt is found in the sea), but the second could be misinterpreted (how much sea salt is found somewhere, not necessarily in the sea).

What's the difference between these examples? Probably that "atmospheric carbon monoxide" must be "in the atmosphere" so you can phrase it either way and convey the same meaning, whereas "sea salt" may be found in the sea or elsewhere.

On the test, use your judgement. When in doubt, choose the clearer phrasing, even if it is longer.

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Emily Sledge
Instructor
ManhattanGMAT

In choice C -

"Levels of atmospheric carbon monoxide increased sufficiently during the twentieth century to begin trapping heat radiating from the Earth, causing the average surface temperature to rise."

it seems to me that "the levels of atmospheric carbon dioxide" will begin to trap heat when they increase in, lets say, value or quantity.

someone also mentioned in earlier posts that, to them, it seemed that the levels increased sufficiently so as to begin trapping heat.

Both scenarios are nonsensical.

Please explain what "takeaway" we are missing here.

Thanks in advance for your comments...

i'm going to respectfully decline your request. i see nothing nonsensical in the correct interpretation of the correct answer. You're going to have to be more specific about what you see as the problem..

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Tim Sanders
Manhattan GMAT Instructor

Sorry to open up a thread that has long been closed.

I too had a doubt about 'C' exactly for the reasons mentioned here.

"Levels of atmospheric carbon monoxide increased sufficiently during the twentieth century to begin trapping heat radiating from the Earth, causing the average surface temperature to rise."

Here the option says - levels increased to begin trapping.

Can this interpretation be correct all the time ?

In the post

agatha-christie-sc-problem-from-cat-2-t9229.html

I understood that option 'B' was incorrect because

She dint use her travel "to" inspire her work.

I may be quoting different examples, which are not relevant to each other, but I 'am a little confused here on the use of infinitive in both the cases.

Instructors please help

You’re missing one important ingredient – the word ”sufficiently”. To say the levels increased sufficiently to begin trapping is appropriate – and very different from saying the levels increased to begin trapping..

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Tim Sanders
Manhattan GMAT Instructor