97.
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
正确答案是B
我的疑问是C选项
笔记上的解释是：
使用which作非限定定语从句,导致逻辑错误,表明所有的chemical pollutants都 have gone virtually unregulated（但是原句也没说到底是不是所有的chemical pollutants啊~？）;
第二个they有指代不清的嫌疑,既可能指代第一个they所指代的Industrialization and modern methods of insect control又可以指代chemical pollutants；（正确选项中的划线部分外的they指代什么呢？）
另外，
Having done可以做后置定语么？
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