请问下NN,there be比较结构的省略(Prep 1-112，128笔记

刚刚在看新prep的笔记，1-128后面有这么一段补充说明，提到there be的比较结构...112题也是there be的比较，但是说是主谓一致，are可以省略，如果这样的话，128题中出现的there be比较结构，助动词不能省是什么意思呢？

128.       (31324-!-item-!-188;#058&004419)

补充说明：比较-主语比较

对主谓宾全的句型主语比较：A do sth than B do.（AB为对等名词，加do是为了显示这是一个可以发出动作的名词，因而确定是主语，进而确定是主语对比）。时态要据后定。There be 句型等同于一般的主谓宾俱全的句型。

主语若相同，可省，但助动词不能省。

112.       (30491-!-item-!-188;#058&004240)

Though certain breeds of dog are renowned for their sense
of smell, there is often a greater difference in scenting ability between
two members of a single breed as there is between members of different
breeds.

(A) is often a greater difference in scenting ability
between two members of a single breed as there is

(B) is often more difference in scenting ability between
two members of a single breed as to find one

(C) is often a greater difference in scenting ability
between two members of a single breed than

(D) are often greater differences in scenting ability
between two members of a single breed as there are

(E) are often greater differences in scenting ability
between two members of a single breed than there is

占位，过会来

这里的比较对象不一样吧

助动词是1.表语态（被动），
        表时态，表否定
        ，构成疑问，以及其他语气词如be, have, do, shall, will, should, would

原则：1.在不影响意思的情况下，可以省略相同部分。

      2.助动词往往可以影响句意思，所以不能省略，也有省略的情况。比如prep1-87

Prep1-128:

According to a study published in The New England Journal of Medicine, aspirin prevents blood clots just as well as a commonly used and more expensive blood-thinning drug does.

 Does补出

Prep1-87

Results of a United States study published in the Annals of Internal Medicine have shown that college-educated women and women living in the South and West are significantly more likely to use supplemental hormones than women living

 Are 没有补出
            

Prep1-112

Though certain breeds of dog are renowned for their sense of smell, there is often a greater difference in scenting ability between two members of a single breed than between members of different breeds.

省略了

Prep1-50

Many teenagers undergo stress, but results of a recent study indicate that the patterns of stress that girls experience are more likely to result in depression than are those that boys experience.

Are 没有省略

My upload speed is bigger than should be

华尔街日报上找个这个例子:

This will, perhaps, have to be judged on a different standard than might be the case in this country,"

might be 在这里不可以省略。

但是，假如不表示推测语气的话，可以省略。

多谢提醒..are 在.prep1-87里不是助动词