prep98 THEY指代，VING表结果，平行

有理想没有钱

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

本题答案是C，原因是STH DO WHILE DOING固定用法，条件是公用主语。但是我当时做题不知道这，我直接从对称角度，我就看了A和C, 然后发现C里面的WHICH指代POLLUTANTS可能有问题，因为中间夹杂了AT THE SAME TIME, 所以果断选A。 A的HAVING的主语是INDUSTRILATION AND MODERN。所以我一直觉得A没错，请好心人帮忙解答下，谢谢。。。。