再问指代问题，prep 19

19. 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

对答案没有疑议，想请nn确认下，since they were developed more than 50 years ago. 中的they到底指代的是什么。

我的想法是since句从层次上来讲应该是 Industrialization and modern methods of insect control have improved ...的时间状语从句，因而they指代的是methods。while句之所以用省略形式，就是为了避免，在while they have introduced some 100,000 dangerous chemical pollutants...since 结构中，they可能指代pollutants的歧义。

不知道我有没有说清楚，请NN们帮我解惑！谢谢

我觉得THEY不可能指代POLLUTANTS吧。无论从逻辑还是语法，都是优先指代从句WHILE中出现的主语，也就是省略的THEY

这道题我这么考虑，

while后面带的其实是从句：subordinate clause.附属于have improved....级别上弱于have improved....

而since实际上是修饰主句：have improved....., since.....所以they应该指代的是主句主语。