156. Dirt roads may evoke the bucolic simplicity of another century, but financially strained townships point out that dirt roads cost twice as much as maintaining paved roads.

(A) dirt roads cost twice as much as maintaining paved roads

(B) dirt roads cost twice as much to maintain as paved roads do

(C) maintaining dirt roads costs twice as much as paved roads do

(D) maintaining dirt roads costs twice as much as it does for paved roads

(E) to maintain dirt roads costs twice as much as for paved roads

This sentence compares the costs required to maintain two kinds of roads. B, the best choice, is able to maintain parallelism in the comparison as well. Choice A incorrectly shifts the meaning by comparing the cost of dirt roads with the cost of maintaining paved roads. Choice C does the opposite: it compares the cost of maintaining dirt roads with the cost of paved roads themselves. Choice D further confuses the sentence by adding a nonparallel clause, it does for, in which it has no clear referent. Choice E introduces the infinitive phrase to maintain... and wrongly attempts to complete the comparison with the nonparallel prepositional phrase for....

昏了，问个弱弱的问题。

C答案中do 为什么不能指代maintaining呢？