Sentence Correction

Can someone please explain the grammatical rule in solving the following question.

The guiding principles of the tax plan released by the Treasury department could have even a greater significance for the economy than the particulars of the plan.

a. even a greater significance for the economy than
b. a significance that is even greater for the economy than
c. even greater significance for the economy than have
d. even greater significance for the economy than do
e. a significance even greater for the economy than have

OA: D

A, B - incorrect grammatically, both answers compare a clause with a noun phrase
C, E - incorrect, the form "do" should be used instead of "have"
D - correct

hi Kasia,

Plz, can u explain more about 'do' and 'have'.

I think both of them are correct.

Regards

Ratnakar Chitturi.

"Have" is used as a conjugated verb and "do" is the so-called helping verb. Helping verbs have a purely grammatical function - they show what tense a given sentence is in but they don't influence the meaning e.g.
Do you have a dog?
I have never been to New York.

In the question discussed above we should use "do" instead of "have" because the second part of the sentence is elided which calls for the use of the helping verb instead of the full conjugated form.
Compare:

answer D (elided version)
The guiding principles of the tax plan released by the Treasury department could have even greater significance for the economy than do the particulars of the plan.

What would answer D look like if not elided:
The guiding principles of the tax plan released by the Treasury department could have even greater significance for the economy than could have the particulars of the plan.

We use ellipsis to make the sentence more concise and to avoid repeating the same verb.