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
A: 两个they不是指代同一个对象
B: correct
C: 两个they不是指代同一个对象
D: but不能引导条件状语从句
E: 同上
注意：
1、 出现两个选项一个有代词，一个没有代词，需要比较代词是否有指代错误或重复
2、
条件状语从句的省略
When/while（时间）/if/unless（条件）/even though/even if/although（即使）/once＋名词/形容词/完整句
这是PREP语法笔记里面的解释,我不明白 D: but不能引导条件状语从句 这个解释,是我不懂某个知识点么?? 为什么说条件状语从句?
我想他说的是时间状语从句的省略吧
while可以加introducing
但是but只能加完整句子
讨论：
c, d的at the same time放在后面，修饰introduce，意思变了吧？
原文是说在improve的同时带来了1000000 pollutants
把at the same time后置，意思是100000 pollutants是同时(exactly the same time)引入的。
我也觉得A的俩个they都是指“methods"
另外，B中while introducting的逻辑主语是谁？按这个句子结构是“the globe" 好像和逻辑主语不一致吧？就想prep15
15. Recently documented examples of neurogenesis（神经形成）, the production of new brain cells, include the brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that learn new songs.
A. the brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that
B. mice whose brains grow when they are placed in a stimulating environment or canaries whose neurons increase when they
C. mice's brains that grow when they are placed in a stimulating environment or canaries' neurons that increase when they
D. the brain growth in mice when placed in a stimulating environment or the increase in canaries' neurons when they
E. brain growth in mice that are placed in a stimulating environment or an increase in neurons in canaries that
A: when placed的逻辑主语是production而不是邻近的mice，句意错；动名词growing和increasing应该改成名词growth，increase
B: they指代不明，可以指代brains或mice；第二个they和第一个they不是一个对象
C: they指代brains不对；第二个they和第一个they不是一个对象
D: when placed的逻辑主语是production而不是邻近的mice，句意错；
E: correct
Google 原句
Industrialization and modern
insect
control
have, according to this story,
improved the quality of life around the globe, but they
have also added some 100,000 chemical compounds that, some scientists worry, could affect the health of people and wildlife. The story says that these persistent organic pollutants, known as POP's,have gone virtually unregulated since they were developed more than 50 yearsago,
第一个they指methods，第二个指pollutants
Google 原句
Industrialization and modern
insect
control
have, according to this story,
improved the quality of life around the globe, but they
have also added some 100,000 chemical compounds that, some scientists worry, could affect the health of people and wildlife. The story says that these persistent organic pollutants, known as POP's,have gone virtually unregulated since they were developed more than 50 yearsago,
第一个they指methods，第二个指pollutants
在GMAT语法中相同代词指代同一对象----是不允许的.
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