Sentence Correction

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 read why b) is correct. However, I am not able to understand how 'improved' and 'introducing' are parallel. To me have + improved is not a participle but present perfect tense. Any thoughts ?

MGMAT discussion thread: https://www.manhattangmat.com/forums/ind ... -t460.html

I am not sure why this question was not raised. I believe that I am missing some concept.

e..g I have done my homework five times. => Have done = present perfect tense

Thanks

The use of "while" calls for the "ing" form of the verb. For example "he can sing while chewing gum", or "she was texting while driving". (The latter is practically a no-no, but grammatically correct.)

between A and B.

A having gone ....they .... the usage of they does not have a clear antecedent.They can refer to either Indus.. and mod..methods or to pollutants.
More so introducing is a result of the improvement. Hence present participle format is correct.
Voodoo child worked for GMAT,'studying' harder and harder day by day.
So A is POE'ed.

B has the proper usage of participle form and the relative pronoun that form. Hence the OA.