Help!!!

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

 answer is D, why not C?

very very confused!

这道题在prep语法笔记中有很好的解释

1.not  but 结构 其实是   ， A be not sth, but (be) sth, 第二个BE可省略,此处BUT是连词，

2.选项C中的BUT与NOT,由于被插入语隔开了，所以可能存在but，可能存在做介词的可能性，but sth,作介词是除了什么。

例如： all students did homework but someone.