请教关于while，何时表示伴随何时表示转折。。。

白冬冬

The continental United States receives an average of 30 inches of precipitation a year; transpiration from soil and from plants returns approximately 21 of the 30 inches to the atmosphere, while the balance of 9 inches contributes to the flow of streams and rivers.

(A) transpiration from soil and from plants returns approximately 21 of the 30 inches to the atmosphere, while the balance of 9 inches contributes to the flow

(B) even though transpiration from soil and from plants returns approximately 21 of the 30 inches to the atmosphere, the remainder of 9 inches contribute to the flowing

(C) although transpiration from soil and from plants return approximately 21 of the 30 inches to the atmosphere, the balance of 9 inches contribute to the flowing

(D) with transpiration from soil and from plants to return approximately 21 inches to the atmosphere, the rest of the 9 inches contributes to the flow

(E) as transpiration from soil and from plants return approximately 21 of the 30 inches to the atmosphere, the rest of the 9 inches contribute to the flow

oa：A

这道题，我看了A的while 就排除掉了。。。因为我的错题里有下边这道 ⬇️

97. Although the first pulsar, or rapidly spinning collapsed star, to be sighted was in the summer of 1967 by graduate student Jocelyn Bell, it had not been announced until February, 1968.

A. Although the first pulsar, or rapidly spinning collapsed star, to be sighted was in the summer of 1967 by graduate student Jocelyn Bell, it had not been announced until February, 1968.  

B. Although not announced until February, 1968, in the summer of 1967 graduate student Jocelyn Bell observed the first pulsar, or rapidly spinning collapsed star, to be sighted.  

C. Although observed by graduate student Jocelyn Bell in the summer of 1967, the discovery of the first sighted pulsar, or rapidly spinning collapsed star, had not been announced before February, 1968.  

D. The first pulsar, or rapidly spinning collapsed star, to be sighted was observed in the summer of 1967 by graduate student Jocelyn Bell, but the discovery was not announced until February, 1968.  

E. The first sighted pulsar, or rapidly spinning collapsed star, was not announced until February, 1968, while it was observed in the summer of 1967 by graduate student Jocelyn Bell.

oa：D

Ron 和OG 都有说这道题－E的while 用法不合适，在句中的while，多表示当。。。时。放在句首才是转折的意思

所以。。。关于while 的用法，到底要怎样呢 。。。

白冬冬

顶一下～

医生吃鱼

while有两种用法：

1、GMAT中主要用法：表示对比，可以放在句中，也可以加at the same time。
TN23-Q21：Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time introducing some 100,000 dangerous chemical pollutants that have  gone virtually unregulated since they were developed more than 50 years ago.
While在句首表对比的例句太多了。

2、少见用法：表示同时发生的动作。