prep中代词指代的原则讨论

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优先作为主句的状从，placed逻辑主语是examples而不是邻近的mice，句意错；根据原文逻辑意思是增长的结果而不是过程，所以动名词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（关于此点，个人认为多个相同代词应该指代同一对象应该是限定在同一主句内；代词指代是否应优先限定在句子部分内，如此题的定从内，不同的从句内的代词如非有同一主句应该可以指代各自不同的主句主语对象；如第一个they在第一个定从内的状从里，应优先指代定从内的主句主语brains产生逻辑意思错误，第二个they优先指代其所在定从内的主句主语neurons同样产生逻辑意思错误）。

C: they指代brains不对；第二个they和第一个they不是一个对象（参考B的个人观点）。

D: when placed的逻辑主语是production而不是邻近的mice，句意错；they的指代错误，they应该指canaries，但这里是所有格，无法指代，将使得they指代neurons等造成逻辑错误。

E: correct，留意that are placed是为了和后面的that learn形式上平行，否则应该省略为placed更简洁；原文有状从和定从两种，所以改为that定从不算改变原文。

注意：句意理解清楚才能选出答案，而不能仅依赖语法结构的形式平行

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；原句while从句和since从句各有一个they，且均为主句的状从，所以两个they应指代相同的主句主语methods，导致since状从逻辑意思错误；having在句末有作伴随或结果状语的可能。

B: correct；改为that定从修饰pollutants使得since从句变为that从句内的状从，所以since状从内的they优先指代其所在主句that定从的主语that，也即对应指代pollutants，逻辑意思合理。

C: 两个they不是指代同一个对象，根据上面推理，这个选项似乎也对？还是因为第二个they在which定从但此定从却是修饰while状从的pollutants，所以应与while状从里的第一个they属于同一主句内，只能指代同一对象，导致出现逻辑错误？还是可能这个推理和15题想法都错误？？

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（让步）/once＋名词/形容词/完整句