7.  Each year companies in the United State could save as much as $58 billion annually by preventing illness among employees and gain as much as $200 billion through improving performance of workers if they simply provided offices with cleaner air.

 A.　annually by preventing illness among employees and gain as much as $200 billion through improving performance of workers if they simply provided

B.　annually if they prevented employee illness and gain as much as $200 billion through worker performance improved by simply providing

C.  annually in employee illness prevention and gain as much as $200 billion through worker performance improved by simply providing

D. in employee illness prevention and gain as much as $200 billion through improving performance of workers if they simply provided

E. by preventing illness among employees and gain as much as $200 billion through improved worker performance if they simply provided

答案选E。但大家觉得E中这两块对称吗 ?

我觉得E选项中，by后边是动宾结构，而through后边是名词短语，显然并非最佳答案。可能指

示比较下来较好的答案。如果改成by preventing illness among employees

and gain as much as $200 billion through improving performance of workers if

they simply provided 应该就更好了。大家同意吗 ？

这个问题不会存在阿，之前的除了employees是复数就是companies是复数了，前者很明显不适中心词，代词怎么会睬他？  所以就是指代后者阿

E还有两个好处，1.动词形式优于抽象名词    2.-ed分词优于-ing分词