新东方补充教材section11,第6题

gustav

6. 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

答案是D，想问than后面助动词补出为什么不是could或者是have，而是do?