不是。。。而是。。。 结构的问题

Is this structure correct?

A is not ..., but ... (wrong)

                  but is ... (right)

According to

74.        (28503-!-item-!-188;#058&003635)  C    D

Paleontologist Stephen Jay Gould has argued that many biological traits are not the products of natural selection, favored due to their enhancement of reproduction or survival, but that they are simply random by-products of other evolutionary developments.

(A) due to their enhancement of reproduction or survival, but that they are

(B) due to the reproduction or survival they enhance, but they are

(C) because they enhance reproduction or survival, but

(D) because they enhance reproduction or survival, but are

(E) because of enhancing reproduction or survival, but are

but的用法，but做介词，表示除了。。。。例如：no one has read it but the students.

或者在词组not….but…中，做连词表示不是，而是的意思。 the plan caused not prosperity but ruin.

c 选项 but 容易产生歧义

不太明白为什么C错？

平行的，be动词放在not前面是一种习惯，are not...but...这个结构既可以把be动词看做在并列之内，也可以看做不在并列范围内。
这是个老问题了，我一直觉得prep里面对C的解释有点问题：
but前面有逗号，不会引起修饰reproduction or survival的含义，而是引起跟favored because they enhance reproduction or survival一起修饰 products of natural selection的歧义（but做介词）。也就是说but simply random by-products of other evolutionary developments作为介词短语作状语修饰其最近的分句they enhance reproduction or survival去了。(而合理的理解是仅仅favored做后置定语修饰products of natural selection, but引导的是并列结构与not…平行，两种理解语法上都没有问题。)