Industrialization and modern methods of insect control have improved

The short answer is that because "while" is not a simple parallelism trigger (like "and"), parallelism is not strictly required when using "while."

Check out this post for more on that, and let us know if you still have questions!
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I can reach answer B by using POE. But one thing makes me confused. Are while and at the same time not redundant?
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Check out this post from earlier in the thread for a not-so-satisfying response to your question!
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Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time they have introduced some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.

(A) while at the same time they have introduced some 100,000 dangerous chemical pollutants, having

- 'having' modifies the entire preceding clause. The subject of the preceding clause is the subject for the participle. In this case 'having' modifies industrial methods. This is not the intended meaning -- the chemical pollutants, not the industrial methods, have gone unregulated!

(B) while at the same time introducing some 100,000 dangerous chemical pollutants that have

- Correct

(C) while they have introduced some 100,000 dangerous chemical pollutants at the same time, which have

- 'at the same time' is a misplaced modifier. As a result, 'which' does not properly refer to anything in this sentence.

(D) but introducing some 100,000 dangerous chemical pollutants at the same time that have

- 'but' is a coordinating conjunction that requires parallelism. "have improved" is a verb and "introducing.." is a participle. NOT parallel.

(E) but at the same time introducing some 100,000 dangerous chemical pollutants, having

- 'but' is a coordinating conjunction that requires parallelism. "have improved" is a verb and "introducing.." is a participle. NOT parallel.
- 'having' modifies the entire preceding clause. The subject of the preceding clause is the subject for the participle. In this case 'having' modifies industrial methods. This is not the intended meaning -- the chemical pollutants, not the industrial methods, have gone unregulated!
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Hi sayantanc2k

Hope you re doing good. Can you help in couple of things ?

1) Do you think usage of which is wrong in option C? I'm doubtful because of the verb HAVE, which should refer to a plural noun pollutants in this case
2) What kind of meaning error are we encountering by misplacing modifier at the same time in C?
3) Why is B preferred over C? Don't you think while is used in temporal sense? While & at the same time : shouldn't they be redundant.

Hello CRACKGMATNUT,

We hope this finds you well.

Having gone through the question and your queries, we believe we can help resolve your doubts.

In order:

1) In Option C, the use of "which" is incorrect, as it is used to refer to information that is vital to the core meaning of the sentence -- that the 100,000 dangerous chemical pollutants have gone virtually unregulated since they were developed; please remember, “that” is used to provide information needed to preserve the core meaning of the sentence, and the “comma + which” construction is used to provide extra information.

2) The construction "introduced some 100,000 dangerous chemical pollutants at the same time" incorrectly implies that all 10,000 chemical pollutants were released at the same time; the intended meaning is that industrialization and modern methods of insect control have improved the standard of living around the globe, and at the same time, they have introduced some 100,000 dangerous chemical pollutants.

3) You are correct that the use of "while" alongside "same time" is redundant, as they are both used to indicate that the given actions are simultaneous, however, redundancy is NOT a deal-breaker on the GMAT. Redundancy/Awkwardness is the least serious of all flaws on GMAT sentence correction; an answer choice can easily be redundant but still the right answer if the other options have concrete errors. Redundancy can only be used to eliminate an answer choice if it is otherwise error-free, and there is a more concise answer choice. In this case, C has clear meaning and modifier errors that call for its outright elimination.

To understand the concept of "Which" Versus "That" on GMAT, you may want to watch the following video (~2 minutes):



All the best!
Experts' Global Team
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GMATNinja, can you please clarify on the basis of what we should eliminate A?

Take another look at (A):


Notice that "having" follows a clause and a comma, so it should be describing the entire previous clause. But that doesn't make sense here. The absence of regulation isn't the result of improving the standard of living around the world!

The only thing that could have gone unregulated is the noun "pollutants," so it's more appropriate to use a noun modifier to describe those pollutants.

That's exactly what we get in (B): "chemical pollutants that have gone virtually unregulated."

If (A) has a modifier problem and (B) fixes that modifier problem, (B) is better.

I hope that helps!
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Is it acceptable to say that ''while'' doesn't demand parallelism, but ''but'' demands parallelism? Thus, Option D and E breaks the parallelism rule, which is, however, not applicable for ''while'' construction.

Thank You
Vighnesh

Good observation. As many experts have pointed out, while is just a subordinating conjunction.
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Hi Experts

GMATNinja KarishmaB MartyTargetTestPrep



Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time they have introduced some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.


(A) while at the same time they have introduced some 100,000 dangerous chemical pollutants, having

(B) while at the same time introducing some 100,000 dangerous chemical pollutants that have

(C) while they have introduced some 100,000 dangerous chemical pollutants at the same time, which have

(D) but introducing some 100,000 dangerous chemical pollutants at the same time that have

(E) but at the same time introducing some 100,000 dangerous chemical pollutants, having

Hi Experts

GMATNinja KarishmaB MartyTargetTestPrep



Why option C is wrong?
Which can modify checmical pollutants so that is not wrong
Is there a meaning change between B and C?
and Is there any grammatical mistake in option C?

First of all, here is a bit about the 'while' adverbial clause from my book:




Look at the main point of the original sentence now.

A and B have improved the standard of living while at the same time introducing many pollutants that have gone unregulated since they were developed more than 50 years ago.

The point is that A and B have done some good but at the same time, they have had some ill effects too.

(A) while at the same time they have introduced some 100,000 dangerous chemical pollutants, having

'having gone unregulated' is perfect participle that makes us expect another action.
Having gone unregulated for so long, the average concentration of pollutants in rivers has reached dangerous levels.
It gives a cause for an effect.

(B) while at the same time introducing some 100,000 dangerous chemical pollutants that have

uses while adverbial phrase 'while introducing ...' because the subject is the same.
Uses a 'that clause' to talk about the pollutants. All good.

(C) while they have introduced some 100,000 dangerous chemical pollutants at the same time, which have

The pollutants have not been introduced at the same time. Here it seems that the 100,000 dangerous chemicals were introduced at the same time.
We want to say that the action of introducing was done at the same time as the action of improving the quality of life.

(D) but introducing some 100,000 dangerous chemical pollutants at the same time that have
(E) but at the same time introducing some 100,000 dangerous chemical pollutants, having

'but' needs a clause. We cannot use a participle with 'but.'

Also, in (D), 'at the same time' modifies intro of the 100,000 chemicals.
In (E), 'having gone unregulated' is used.
These are the same errors as found above in options (C) and (A).

Answer (B)
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Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time they have introduced some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.

Option Elimination -

"While" can be used to introduce participle phrases. "While" connects the "participle phrase" to the main clause of a sentence, indicating a simultaneous or contrasting action. Here, "simultaneous" action is important. When "While" is used to introduce a participle phrase, it indicates that the action described in the participle phrase is happening at the same time as the action in the main clause.
For example, While waiting for a bus, Sarah read a book. Or John Sang a song while playing a guitar. Or a contrasting action at the same time e.g. While cooking dinner, she listened to music.

Unlike "But," "while" can be used to introduce subordinating clauses or participle phrases.

(A) At the same time, they have introduced some 100,000 dangerous chemical pollutants, having the first "they" refer to "Industrialization and modern methods" while the 2nd "they" refers to "chemical pollutants." For "having," normally, the structure is "Having finished his work, John went for a walk" - the action of finishing work happened before John went for a walk. Present perfect participle is used to indicate an action that occurred before another past action (different from past perfect - in past perfect, the action has been completed in the past before another past action, but in present perfect participle, the effect of that action (that occurred before another past action) is present). Here, after "Having won," there is no other action.

Here, "having" while making sense with the "introduced some 100,000 dangerous chemical pollutants" doesn't make sense with "Industrialization and modern methods of insect control have improved the standard of living around the globe." So two issues, "they" and "having."

(B) while at the same time introducing some 100,000 dangerous chemical pollutants that have - - Here, the introduction of some 100,000 dangerous chemical pollutants has been happening at the same time Industrialization and modern methods of insect control have improved the standard of living around the globe. So the use of while is correct. The use of "that" is okay to introduce the essential information.

(C) while they have introduced some 100,000 dangerous chemical pollutants at the same time, which have - here there are a couple of issues. To show the simultaneous nature, we need a participle phrase. Moreover, to some extent, the use of "they" is ambiguous. They can refer to "Modern methods" or "Industrialization" and "Modern methods." Also, which can either refer to time or pollutants, though reference to pollutants makes more sense. Additionally, "At the same time" is a misplaced modifier because "Modern methods" or "Industrialization" didn't introduce the pollutants in one single moment just like that. The sentence means that as "Modern methods" or "Industrialization" improved the living standards, they also introduced chemical pollutants (in the same 50 to 100 years time).

(D) but introducing some 100,000 dangerous chemical pollutants at the same time that have - unlike "while" but needs a clause after it. Wrong.

(E) but at the same time introducing some 100,000 dangerous chemical pollutants, having - unlike "while" but needs a clause after it. Wrong.