请教一道Prep破解版-97

Prep破解版97

Industrialization and modern methods of insect control have improved the standard of living ar

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 ag

(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 timewhich 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

答案是b，我选a。我觉得a中的they指代没有问题，也很对称，错只错在最后having gone上了。而b，破解版中说while引导从句时,如主从句的主语一致,且从句谓语又含有be,则从句主语和be可省略。可是该题中没有出现be 结构，省略就觉得有点问题。此外，主句中有have做助动词，难道b选项中省略的是have been么？请牛牛指教？

明白了，谢谢！