Interesting questions. Let's see what I can do.
1) Almost anything can be omitted if it makes sense, but the issue is usually structural. Consider the following:
I ate more popcorn than my brother.
Is there any ellipsis going on here? The “full version” of this sentence is not proper English:
I ate more popcorn than my brother ate popcorn. (This just doesn’t fit the structure we expect with “more than.” We’d only use this if we were comparing two different things, and then there’d be no room for ellipsis: “I love music more than my brother loves popcorn.”)
We could say this:
I ate more popcorn than my brother ate.
This doesn’t seem flat-out wrong, but it’s not the normal usage. We’d be more likely to see this:
I ate more popcorn than my brother did.
Here, the word “did” stands in for the previous verb (ate). Now the question is, do we need that “did”? Looking back at the original sentence, there’s no ambiguity. Even if we were inclined to think I might eat my brother, there’s no way to read the sentence to produce that meaning. In fact, the GMAT is not going to like either of the last two sentences, because the “more than” comparison is really between me and my brother. (See the explanation for SC 38 in the 2nd ed Verbal Review.) So really, we can say there’s no ellipsis here.
Now, in other sentences, some additional language is needed. How about this?
I admire the president more than my grandfather.
What does this mean? Do I think more highly of the president than my grandfather does, or do I think more highly of the president than of my grandfather? Here, additional structural words can fix the ambiguity:
Interpretation 1: I admire the president more than my grandfather does.
Interpretation 2: I admire the president more than I do my grandfather. (This works, but it doesn’t sound great. Since “admire” is just one word, I’d be tempted to repeat it, but the GMAT likes to avoid that kind of repetition, in part to make the answer less obvious.)
Again, the word do/does/did can stand in for a verb, similar to the way the pronouns that/those stand in for nouns. In Interpretation 1, we left out several words, but they were all “contained” in the word “does.”
A few other examples (note the use of structure to make the meaning clear):
Adjective: Don’t say you’re diabetic if you’re not. (Parallelism between “you’re diabetic” and “you’re not [ diabetic].”
Modified adjective: Don’t say you’re allergic to wheat if you’re not [allergic to wheat].
Modified noun: The inflation-adjusted grosses for these films are greater than those of many recent blockbusters. [those = the inflation-adjusted grosses]
One might argue that so far only the adjective examples have represented true ellipsis, as in every other case there is a substitute word filling the hole. So let’s look at your 2nd question.
2) There is nothing grammatically wrong with saying “Rohit’s is an office . . .” However, this is not a construction I’d recommend. This usage does work in some circumstances (“Ours is a happy marriage.”), but it’s kind of a stylistic flourish that must be used with care. (Why not just say “Rohit’s office is staffed by high-quality professionals” or “We have a happy marriage”?) I don’t think I’ve seen this on the GMAT.
3) The words “have” in Q1 and “were” in Q3 work the same way as do/did/does. “Did” is a stand-in for verbs in the simple past tense, and “have” and “were” stand in for verbs in the present perfect and past progressive, respectively.
4) It’s fine to use “were” to replace a verb originally introduced by “are,” and vice versa:
My dogs are hungrier now than they were this morning.
My dogs were more playful when they were puppies than they are now.
(Note that “they were”/”they are” can’t be dropped, because we start the comparison with “my dogs,” and we can’t compare “my dogs” to “this morning” or “now.” By adding “they were”/”they are” we create a comparison between clauses.)
5) For the charter vacations problem, we can’t compare “they cost” to “they seemed,” because those verbs don’t play the same role. We’re not saying that they did one thing (costing) more than another (seeming). Also, most verbs do not work as stand-ins. “Did/does/do,” “have/has/had,” “are/was/were,” and “had” are special. That’s one reason why we don’t say “I ate more popcorn than my brother ate.” The more add-ons to the verb, the worse it is: “I oversaw the production of more vehicles than my brother saw.” (“Did” at the end would be fine.)
Note that in the “flourished” problem, the idiom is “at the same time as.” This works kind of like “along with” or “in tandem with”: This civilization flourished in tandem with those civilizations.
If we had “at the same time that,” we’d need a clause with “did” at the end.
I hope this helps. Let me know if I can clarify anything!
Dmitry Farber | Manhattan GMAT Instructor | New York
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