一道PREP 语法题，不解

43. 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.

C because they enhance reproduction or survival, but

D because they enhance reproduction or survival, but are

答案是D，不解，因为 are not the products of ...., but simply random  by-products 不已经很清晰了吗？ 为什么一定要加are?

58. Diesel engines burn as much as 30% less fuel than
gasoline engines of comparable size, as well as emitting far less
carbon dioxide gas and far fewer of the other gasses that have been
implicated in global warming.

A  of comparable size , as well as emitting far
less carbon dioxide gas and far fewer of the other gasses that have

A 就是正确答案，但 “the other gasses”这里为什么是对的呢， the other 后面，不应该只用单数吗

The other 之后不是只能用单数。

第一题加了are是为了避免和前面favored的部分产生混淆。因为but还有only的意思。如果不加are的话也可以混淆理解为reproduction or survival is simply by-products of ... Then again, 如果没有插入语不用are肯定是更加简洁。但是记住cardinal rule: cause no confusion.