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（D）

(E) a significance even greater for the economy than have

为什么是用do来连接呢 不是应该用could吗？

If you just use 'could', your sentence will be incomplete since you actually need 'could do'.

When u use 'could do', it's redundant.

The solution is to use 'do' to replace 'could do'.