请教PREP第一套的97题

97.   (29753-!-item-!-188;#058&003991)

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

答案是B, 我认为A对。

while at the same time ...从句里面的谓语动词应该与主句用的一样啊！因为是at the same time.表明同时发生的！

请各位高人帮我指点一下！！！

谢谢了

这是while引导分词的用法！表示一种伴随的状态。

I like to read book , while listening to MP3.

B中的they指代的是什么？