【提问】一道prep上的题

zcooles

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

MarilynR

说错了，记不太清了。刚看了笔记说是 主语一致，时态一致时省略，明天我找到一个这种题再看看吧。

zcooles

但是这里v好像不一样诶，前面只出现过have improved,不用be动词也可以么？

MarilynR

比如SVO,whileSVO。当S V 一样是，可以省略为SVO,while doing。的形式

zcooles

答案给的B
我想问的是B中while后面的结构，那个是省略吗？
是不是可以还原成...while they are introducing some...的形式？
如果是这样的话，为什么be动词没有还原呢？
前面并没有出现过be动词呀