In addition, the answer choice A should be ignored for the reason that it introduces ambguity in the meaning ? that is ing modifier modifies methods or pollutants ? Grammatically speaking, this should be applicable to the subject and being an adverbail modifier, should modify the action of the subject of the clause it is modifying. Hence, no ambiguity.

What if I rewrote A :

Having gone virtually unregulated since they were developed more than 50 years ago, Industrialization and modtern 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 .

Thank you for providing deep insight on the above issues .

Could someone explain the above doubts please

Hey, GMATMadeEasy:

Good questions - let me weigh in with a few thoughts.

On C:

1) You're right - the comma splices a subject away from its verb, so that's a problem.

You wouldn't say:

I ran, and swam.

You would say:

I ran and swam. OR I ran the mile in high school and swam the 1500 meters in college.

So you can't have that comma split the subject from its verb in this sentence. You can't say:

...they have introduced pollutants, and have gone unregulated

Without that comma, that would be fixed.

2) This one is more idiomatic and probably less universal (so probably not as important to really know, but worth having seen), but "while at the same time" is a colloquial expression to transition between two things that seem to be in opposition:

e.g. "I made straight As in college while at the same time failing miserably on the GRE and GMAT"

because of its colloquial/idiomatic nature, "while at the same time" as a transition between two somewhat-concurrent but seemingly ironic things doesn't mean the same thing as "at the same time", which literally means "simultaneously".

Choice C places "at the same time" in a way that doesn't fit the colloquial nature:

Industrialization and modern methods have improved the standard of living while they have introduced dangerous pollutants at the same time

That position change of "at the same time" changes the meaning slightly. Instead of "ironically, in the same era" it means 'literally, at the same exact time", and that's an illogical meaning...the precision of that "exactly the same time" isn't something that really makes sense.


3) The subject of the verb "have" at the end of the underlined portion is different in choices A/C/E from B/D.

"Having" in A and E, and "and have" in C link back to the original subject "industrialization and modern methods".

"....pollutants that have" in B and D make "pollutants" the subject of the verb "have gone virtually unregulated.

Honestly, I don't know that you can definitively say that "have gone unregulated" shouldn't apply to "modern methods of insect control", but I'd say that you can probably say that it wouldn't apply to "industrialization". So I think you can make a case for the meaning in A/C/E being illogical, or at least not preferred. In B/D, the sentence makes pretty good sense by saying that the byproduct of this standard of living is pollutants that have gone virtually unregulated.


So between those points I think you can say definitively that C is wrong and that B is correct. I hope that helps...

Point 1 ; coma rule when subject is same . I agree. But if the sentence is big, generally we can use it no ?

Point 2 - > thanks

point 3 - > I really liked the idea that modifier is not applicable to industralization . makes senes .

GMAT is playing too much on meaning in many sentences, not fair . What approach one can use in exam hall ?