关于while以及whereas句子结构的问题

hlhlhlt

看了很多while和whereas的问题，比如论坛上很好地讨论帖
http://forum.chasedream.com/GMAT_SC/thread-35969-2-1.html
以及米国人写的：http://grcpublishing.grc.nasa.gov/WizardArchive/wizard4/wiztext.htm
Match Wits With Our Word Wizards(Illustrated version of Word Wizards)
In each sentence, select the best choice for formal writing:

• While /Although the method is efficient for most applications, it can produce errors when small, irregularly shaped specimens are tested.
  
• Place the sample into the rig while / whereas the power is off.
  
• The Structures Division had responsibility for the fan blade design, while /whereas the Materials Division was to develop the composite material for the blade. (The two projects are not necessarily happening at the same time.)
  
• While /Although the experiment was thermal cycling, an inert atmosphere was maintained to avoid oxidation of the aluminum framework.
  
• The single-crystal material is somewhat stronger, while /whereas the composite is significantly lighter.
  
• Make sure that excessive pressure is not applied while / whereas the surfaces are in contact with each other.
  

For an explanation of while, whereas, and although, see Quirks of English.






我的感觉就是书面表示强对比优先考虑whereas，while口语上也表示对比但是书面上多表示同时发生所以在尊重语义的条件下就要考虑while是否引起歧义了，当然prep也出现了多次while表示对比，选项里没有whereas。

我就是想确认一下结构问题，whereas是否要绝对对称？While就不要求？而且while的逻辑主语和主句主语相同的时候是不是while的主语省掉？

谢谢！！

hlhlhlt

upup!

hlhlhlt

up!