请教PREP2 90

90.
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Diesel engines burn as much as 30 percent less fuel than gasoline engines of comparable size, as well as emitting far less carbon dioxide gas and far fewer of the other gases 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 gases that have

(B) of comparable size, as well as emit far less carbon dioxide gas and far fewer of the other gases having

(C) of comparable size, and also they emit far fewer carbon dioxide and other gases that have

(D) that have a comparable size, and also they emit far less carbon dioxide gas and other gases that have

(E) that have a comparable size, as well as emitting far fewer carbon dioxide and other gases having

这道题目的答案是A，我想问一下as well as不是连词吗？那这里的emitting前面没有和它可以并列的词啊？怎么解释呢？我理解as well as的作用和and是一样的？或者as well as是一个副词啊？谢谢大家。

emitting在这里应该是伴随状语 修饰Diesel engines burn，所以不需要找对称