再来看一道PREP07 SC 牛牛解答

zlljolie

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
这道题目答案最后选择B。想问，B中introducing用的合适吗？如果补全，不是成了they are introducing,可是根据语意来看，后面有have gone unregulated来看，都应该用have introduced呀……这能对吗？
C选项为什么不对？ which非限制性定语从句也没有什么问题呀，从which have的have来判断，肯定是优先修饰pollutants的呀

salle66

以下摘自prep语法笔记：

（B）正确。使用sb. do......while doing 结构，省掉了they，避免了同第二个they产生指代不清的嫌疑，使用限定性定语从句符合逻辑意思。
（C）使用which做非限定性定语从句，导致逻辑错误，表明所有chemical pollutants 都 have gone virtually unregulated; 第二个they有指代不清的嫌疑。

另外，关于while的用法：while引导从句时，如果主从句主语一直，从句谓语又含有be，则从句主语和be可省略。while后可直接跟现在分词、名词、形容词或介词短语。
e.g. We are teachers while (we are) serving as students. 我们边当老师边当学生。

限定性定于从句&非限定性定于从句
限定性定于从句：表示局部概念：例： I am checking up the models who are in black shirts. 表明有很多模特，而我打量的是那些穿黑色衬衣的。
非限定性定于从句: 表示整体概念：例：I am checking up the models, who are in black shirts.  表明这里有一群模特，她们的共同特点是都穿黑衬衣。