[求助]挑战白勇原则的语法题

小弟下面有一道语法题向各位牛人求助

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

prep答案是D

(A) due to +动词的抽象名词形式,表达不够有效；not…but…连接的结构不平行。
(B) due to +动词的抽象名词形式,表达不够有效; they多余, 破坏了 sth/sb be not… but (be)…的结构
(C) but可能作为介词,产生because they enhance reproduction or survival, but simply random
by-products的歧意
(D) 正确，but are表明了but在这里只能作为连词,构成be not… but (be)…的平行结构
(E) because of +动名词形式,表达不够有效

可是D不是有悖于白勇语法下面这个原则吗？并列结构的第二个成分的谓语动词可以省略:两个句子并列,第一个句子含有be动词或
者become,第二个句子中的be动词或者become必须省略,同时,一些重复的名词或形容词也必须省略.

没有are会有歧义