今天做了prep2007,p1,73题，留下了一点疑惑，来CD一看，发现前CDer们已经展开过热烈并且有深度的讨论，附上原帖：
http://forum.chasedream.com/thread-348985-1-1.html
简单的总结如下：
not...but...出现在句子里有两种情况，
第一种正是not A but B的平行结构，在这里面A和B都不是一个完整的句子，
例如：
The apple is not red but green.
A is produced not by B but by C.
而第二种则是A but B的平行结构，只不过在A里面出现了not，因此这其实是完整句子间的平行（B里面省略了主语），
例如：
I do not like girls but like boys.
现在问题来了，
prep1-59. A new genetically engineered papaya was produced not by seed companies who have been motivated by profit, which was the case with most genetically modified crops previously approved for commercial use, but university and United States Department of Agriculture researchers who allowed growers to use it free of charge.
(A) produced not by seed companies who have been motivated by profit, which was the case with most genetically modified crops previously approved for commercial use, but
(B) produced not by profit-motivated seed companies, the case with most genetically modified crops previously approved for commercial use, but
(C) produced not by profit-motivated seed companies, as was the case with most genetically modified crops previously approved for commercial use, but by
(D) not produced by profit-motivated seed companies, which was the case with most genetically modified crops previously approved for commercial use, but was produced by
(E) not produced by seed companies who have been motivated by profit, the case with most genetically modified crops previously approved for commercial use, but by
这题答案选C。也就是说这里是第一种情况——not A but B的平行结构：
A new genetically engineered papaya was produced not by profit-motivated seed companies, as was the case with most genetically modified crops previously approved for commercial use, but by university and United States Department of Agriculture researchers who allowed growers to use it free of charge.(原句）
首先，如果换一种表达方式让它变成第二种情况（如下），在语法的正确性上是不是没有问题呢：
A new genetically engineered papaya was not produced by profit-motivated seed companies, as was the case with most genetically modified crops previously approved for commercial use, but was produced by university and United States Department of Agriculture researchers who allowed growers to use it free of charge.（改动1）
此处but后面省略了主语
另外，这个句子里面not A but B的结构是不是还可以这么说：
A new genetically engineered papaya was not produced by profit-motivated seed companies, as was the case with most genetically modified crops previously approved for commercial use, but produced by university and United States Department of Agriculture researchers who allowed growers to use it free of charge.（改动2）
此处not produced by和but produced by平行，并且共用一个was
如果改动1和改动2在语法上都是正确的话，注意到这两个句子唯一的区别就是改动1里but的后面多了一个was，于是可以得出结论：这个was是可以省略的。
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发表于 2013-8-30 14:20:25
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