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