Industrialization and modern methods of insect

[susan_2013]

Source: GMATPrep test

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

OA is B.
I'm wondering why choic C is not right?
Thx.

[shreerajp99]

C is wrong because as per GMAT,which refers to the noun before comma.In C,it refers to 'time' and that makes no sense.

Thanks,
Shreeraj

[RonPurewal]

hi,
please search the forum before posting, thanks.

the following 2 threads almost certainly contain the answer to your question. if not, post it on one of them, please; don't create new threads for problems that already appear on the forum.

industrialization-and-modern-methods-usage-of-while-and-but-t1871.html

industrialization-and-modtern-methods-of-insect-control-have-t460.html

thanks.