While at same time + Verb-INGis found in GMATPREP. I have also searched some other online newspapers such as nytimes, washingtonpost, and sciencedaily. I have found that while at the same time + verb-ing is an acceptable form.

While at the same time + VERBING is most often used in GMAT. I have seen in GMATPREP sentences. GMAT is a fan of this uses. If you study at least 100 sentences from GMATPREP and make your note by analyzing the patterns of the sentences GMAT likes, I am sure your SC skill will improve dramatically.

Ok, come to the point.

Just by looking the "while at the same time + Verbing", you can guess the answer, but you MUST check other options as well.

Industrialization and modern methods have improved ....pollutants, having gone

The problems in this sentence:

"COMMA + Verbing" modifies the entire preceding clause, and the subject of the preceding clause becomes the subject of the VERBING.

Now, A means that "Industrialization and modern methods have gone unregulated". This is changing the intended meaning of the sentence. E is also in this category.

COMMA + AND + VERB: is correct only when we use a list of more than two verbs, and we should use "COMMA + AND VERB" at last. This kills C.

BUT INTRODUCING is not parallel with any one of the previous verb. This kills D.

They are not going to NY but are going to LA.

Answer is B.

GMATMadeEasy wrote: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 100,000 dangerous chemical pollutants at the same time, and have
d. but introducing some 100,000 dangerous chemical pollutants at the same time that have
e. but at the same time introduce some 100,000 dangerous chemical pollutants, having

I chose B as the better answer. I missed the "parallelism" though. I thought it should have been "introduced" to parallel "improved" in the first line (would read "modern methods... have... improved the standard of living... while at the same time [introduced]".

I guess I'm wrong?

Nice explanation catseye !!! You have suggested a good way to improve SC , i will try to apply that relegiously and will definately let you know the results .. .

For one thing, 'introduced' and 'introducing' are 'grammatically' parallel, since both are used as participles.

An issue with A is the usage of 'having'. 'having', on GMAT (when 'having' is used as a participial phrase) typically introduces a 'sequence' to the events. For example:

Having worked hard for GMAT, he hopes to score well.

In the above sentence, the 'working hard' part is already done (first in the sequence) and 'hopes to score well' is second in the sequence.

By that logic, in the sentence under consideration, the use of 'having' would suggest that the pollutants were 'first' unregulated and 'then' introduced. But in the context of the sentence, this is not true, since the intention of the sentence is to portray that 'un-regulation' and 'introduction' have been 'simultaneous' activities (for the past 50 years).

Great discussion!

I have eliminated the options A and B as soon as I read the question for 'while' and 'at the same time' are redundant. I think that catseye was trying to address this with the following statement in his post.

Catseye, can you post few examples, which would help us understand the concept clearly.

While at same time + Verb-INGis found in GMATPREP. I have also searched some other online newspapers such as nytimes, washingtonpost, and sciencedaily. I have found that while at the same time + verb-ing is an acceptable form.

Thats a great advice. Could you share some more experiences that you had with GMAT prep?

If you study at least 100 sentences from GMATPREP and make your note by analyzing the patterns of the sentences GMAT likes, I am sure your SC skill will improve dramatically.

@Education Aisle,

Your quote was helpful in understanding the parallelism part. Can you clarify whether always can a past participle (VERBed) and present participle (VERBing) be parallel on GMAT?

For one thing, 'introduced' and 'introducing' are 'grammatically' parallel, since both are used as participles.

bubbliiiiiiii wrote: @Education Aisle,

Your quote was helpful in understanding the parallelism part. Can you clarify whether always can a past participle (VERBed) and present participle (VERBing) be parallel on GMAT?

Yes, present and past participles 'can' always be parallel. See few examples below:

Badly wounded but still breathing, the soldier kept saying: Vande Matram.

My old bike, shackled but resounding, never stranded me on road.

...and umpteen others.