大全249 when 和while 到底有什么区别？？

1.        Doctors still know little about how the Listeria bacterium is spread and why the disease it causes, listeriosis, afflicts some people in a contaminated area though it spares many others.

(A) though it spares

(B) where it spares

(C) despite sparing

(D) when sparing（E）

(E) while sparing

249, 补充-175

A, though意思错, 前后不是转折关系。

B, where it spares限定修饰a contaminated area，不能准确表达原意。

C, D,E的比较，因为见到some，others，所以中间用while最能准确表达意思。

while，有与此同时的意思，同时发生的意味，一般ing多一些。J is running while K is sleeping

强调动作的同时发生

when 范围更广一些，同时发生的意味没有while来的重

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  (B)

(E) but at the same time introducing some 100,000
dangerous chemical pollutants, having