一道语法题求问

土豆呀 · 发表于 2017-9-21 17:05:25

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

这道题答案选D，我想问问，not...but...不是应该平行吗？句子前面的 ...are not the products...，but后面为什么还要加are呢？不应该是和product平行吗？

[SC悬赏令] 一道语法题求问

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