SC - parallelism

[aanchalsinha]

Hi could someone please explain why answer B is the correct choice? I can't seem to understand why we need the 'do' at the end.

Thanks

Hand ale pumps may slightly improve the flavor of ale over gas-powered kegs, but modern pub managers contend that hand ale pumps cost twice as much as gas-powered kegs.

A. hand ale pumps cost twice as much as gas-powered kegs.
B. hand ale pumps cost twice as much as gas-powered kegs do.
C. maintaining hand ale pumps costs twice as much as gas-powered kegs do.
D. maintaining hand ale pumps costs twice as much as it does for gas-powered kegs.
E. to maintain hand ale pumps costs twice as much as for gas-powered kegs.

[srihariom]

Hi,

Choice A is comparing the cost of ale pumps to gas powered kegs
whereas

Choice B correctly compares the cost of ale pumps to the cost of gas powered kegs.

Ron,
Can you please correct me if i'm wrong.

[jnelson0612]

What is the original source for this question?

Actually, the reason is that we are using the comparison word "as". "As" is used to compare clauses, which consist of a noun and a tensed verb. So we need to say
hand ale pumps cost twice as much as gas-powered kegs do. (I have bolded the subject and verb)

[aanchalsinha]

I practiced number of these comparisons questions and its pretty obvious to me now that 'do' is required at the end.

Thank you for responding. Source of this question is 800score.com

[jnelson0612]

Thanks!