by michail.palagaschwili Sat Jan 16, 2016 4:55 pm
I've answered this one correctly. Here's is my reasoning, I hope it was not just a lucky shot and the errors found are valid.
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, 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
Comma + ING-Modifier, modiefies preceding clause. This doesn't make sense here, so incorrect
b. while at the same time introducing some 100,000 dangerous chemical pollutants that have
Correct by POE. I've seen many such constructions in the gmat questions while+ ING
c. while they have introduced 100,000 dangerous chemical pollutants at the same time, and have
1. There is no need to separate an adverbial phrase "at the same time" from its verb.
2. "They" refers to "Industrialization and modtern methods" --> They have not gone virtually unregulated. The later refers to pollutants, so incorrect.
d. but introducing some 100,000 dangerous chemical pollutants at the same time that
I'm not 100% sure about this one.
1. Usually you can see a construction while + ING, here "introducing" is not parallel to "have introduced"
2. Also, "at the same time that" --> That modifies the time, and it is better placed in B (right after pollutants)
e. but at the same time introduce some 100,000 dangerous chemical pollutants, having
Again, Comma + ING-Modifier, modiefies preceding clause. This doesn't make sense here, so incorrect
