helping verb omission and comparison

[ZHUOC614]

Hello instructor,

I found these on page 253 of the Manhattan SC guide:

The first instance of the verb should usually match the helping verb in tense. If you need to change
tenses, repeat the whole verb in the new tense.
Wrong: I have never seen an aardvark, but last year my father DID.
Right: I have never seen an aardvark, but last year my father saw one.
In the rare cases in which the tenses do not need to match, the exact verb form missing after the helping
verb should be present elsewhere in the sentence.
Wrong: Our cars were designed to inspire envy, and they ARE.
Right: Our cars were designed to inspire envy, and they DO.


I found these are really great rules, but I really didn't understand what does the rare cases mentioned in the bold face means?

And I am also very confused when I am facing some SC that deal with COMPARISON that some part are omitted. I understand comparison is a kind of parallelism, but I really have difficulty in finding the proper thing that the sentence is intending to compare. Could any experts tell me what I can do to improve?

Thanks in advance!

[RonPurewal]

Hi,

• Questions about material in the strategy guides don't belong in this folder. Please post such questions in the MGMAT non-CAT folder.

• As for your last question, it's not possible to answer such things without specifics.
If you're asking such a question, then there must be some troublesome problem(s) at the root of your question. So, please post questions on the forum about the specific problem(s) in question (in the correct folder, of course).

Thanks.