一、省略结构分析
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
考察比较中的省略结构。
也就是than后面到底是没有助动词，还是加do,或者是have。首先than后面如果有助动词的话，必然是事情和事情的比较，也就是句子间的比较，GMAT语法如果没有助动词就是than前后名词的比较。GMAT考试Do 和have的取舍在于前面的时态，如果前面是一般时态就用do的形式，如果前面是完成时就用have的形式。
这里很显然是事情和事情的比较(principles 和particulars各自have significance的比较)所以需要助动词，因为前面是一般时态，GMAT入门生都知道所以用do,选择D
另外，significance是不可数名词。
二、after的妙用
1 after doing 相关问题
220. (GWD-24-8, OG12-86)The results of the company's cost-cuttingmeasures are evident in its profits, which increased five percent during thefirst three months of this year after it fell over the last two years.
A. whichincreased five percent during the first three months of this year after it fell
B. whichhad increased five percent during the first three months of this year after ithad fallen
C. whichhave increased five percent during the first three months of this year afterfalling
D. with a five percent increase during the firstthree months of this year after falling (C)
E. with a five percent increase during the firstthree months of this year after having fallen
答案选C，但解释上有点问题我不明白：下面是语GMAT语法笔记上对于B和C的解释：
B. after it had fallen时态上没有问题，可以与over the last two years搭配，但是不如after falling简洁
C. Correct;afterfalling简洁，状语从句的省略
求助GMAT考试讨论：可是我不理解为什把after doing理解为状语从句的省略。我觉得这里不是省略!!!
状语从句的省略：从句主语和主句主语一致，并且包含be。。。从句主语和be可以省略。when，although ，等词引导时间状语从句，让步状语从句等时，可以用这种形式来简洁表达。
但是如果把这里的after doing 理解为 after it have/had been falling。我觉得也不能清晰的表达出原文所想表达的时态先后关系。而且如果这里 fall是进行时表达一直在下降，这里也是不对的吧。