To map Earth's interior, geologists use a network of seismometers to

Thanks ExpertsGlobal5, but not sure if I understood. There are numerous official examples in which the modifiers (which or that) don't touch the preceding noun or in which the modifiers don't refer to the immediate preceding nouns. So, how can we make a rule that "option B is wrong just because "which" is "not correctly" modifying the immediately preceding noun.

Consider this official example, as per the logic you stated, the OA must be wrong because "that" is "not modifying" the immediate noun "progress:.

Hi Pankaj0901!

You're right that we definitely have some leeway in applying noun modifiers. The "touch rule" is not an absolute rule. Sometimes we can skip over some modifiers to refer back to an earlier noun, as long as the intent is clear. Here's a case with a few modifiers to skip over (but be aware of the spoiler--it's from an official mba.com exam): https://gmatclub.com/forum/although-she ... ml#p357857

There's even an OG question on which we have to skip over a verb to apply a "which" to the previous noun:
https://gmatclub.com/forum/gusty-wester ... l#p1869067

Now, having said all that, this in no way means that we can just go back and apply the modifier to whatever noun we want. Even this simple sentence is wrong:
My dad wrote a book, who is an expert on poetry.

What's wrong with this? Clearly, the only reasonable referent for WHO is "dad," right? And we're just skipping over the verb and object to refer to the main subject, right? No big deal? Nope. Can't do it. This is really saying that my book is an expert on poetry (and a "who," apparently). Why? First, if we wanted to modify "dad," there's an easy way to do it--just put the modifier next to "dad." Second, even though the clause is short and simple, we have still jumped to the end. This muddies our intent and makes the reader work too hard. We should only attach a modifier as far away from a noun as we NEED to in order to get a clear and logical sentence. In this case, using an adverbial modifier is a clean, easy way out of this problem, and that's a solution we see all the time in SC.

In my earlier comments, I also mentioned that we don't normally stack two noun modifiers on top of each other, and that's another reason to avoid the construction in C. If we wanted to keep modifying waves, then there would be an easy way to do that, too. We could say "waves THAT originate . . . AND THAT travel." Since the author doesn't do that, they are clearly signaling that they are doing modifying waves. That may be one reason that so many of us state so plainly that "which" must apply (incorrectly) to "interior."

Now, there's also a more important reason to go with C. The adverbial modifier is really what we wanted all along! The point of the sentence is not just "Hey, scientists used these waves, and by the way, the waves have variable speed." The point is that we can use the waves to make seismic maps BECAUSE the waves travel at different speeds through different materials. The adverbial -ing modifier conveys this meaning, and the noun modifier does not.

Finally, be careful not to let the letter S fool you on singular vs. plural. Remember that an S at the end of a verb usually makes it singular, not plural! I know you were using the right grammar in matching "travel" with a plural noun, but watch that you don't get mixed up in the terminology. When we say "waves travel," both the noun and the verb are plural, and when we say "the wave travels," both the noun and the verb are singular. Keeping this distinction will help make all our explanations clearer.

GMATNinja

In choice (E), there is no need to add comma before and that, right? >>> interior "," and that travel most rapidly through cold, dense regions and slower
I mean that comma is not another key to eliminate this choice

Thank you DmitryFarber. Your explanation perfectly clarifies my doubt.

GMATNinja
I am not exactly sure where to find this comma ING usage in more detail.
Could you help point out the difference between a compound clause that come before the comma ING. In some cases, I am not sure if the comma ING will actually modify more than just the immediate preceding as shown in this SC. Please see AC-C in this example? The use of AND seems to allow the "the politician decided to postpone" to be modified by the comma ING. However, most responses in that thread showed that distorted the meaning. My question is if you could confirm the compounded structure in this example is what allowed both clauses to be modified, in comparison to the OP of this Sc, in which, only the object of the main clause (seismic waves) is modified.
For instance, https://gmatclub.com/forum/finally-reac ... 60019.html

experts, can someone please help me understand the use of comma with and ? because in option C, there is no comma before "and" how is it correct then ? thanks

Hello Magni03,

We hope this finds you well.

To answer your query, Option C does not require a comma before the "and" because this "and" is linking two elements in a list - the adverbial modifies "most rapidly through cold, dense regions" and "more slowly through hotter rocks"; remember if a list contains only two elements, they must be joined by a conjunction.

We hope this helps.
All the best!
Experts' Global Team

I have a question on what was mentioned above by an expert in that "We can eliminate options A, D, & E because they don't use parallel structure when describing the two speeds a seismometer travels in different conditions."

To clarify, is the use of "more" and "most" part of the parallelism?

Would it be incorrect to say e.g., "interior, traveling rapidly through cold, dense regions and more slowly" or "interior, traveling most rapidly through cold, dense regions and slowly"?

Thank you!

That's correct. The phrase "that originate {...} and that travel" is a parallel list of "that" clauses. These are NOT independent clauses, so we don't need a comma to connect them.

I'm not 100% sure that I'm interpreting your question correctly, but in the example you linked to, the "and" is part of one big clause:

"...politicians decided to postpone by at least five years an ambitious plan to protect wild salmon and other endangered fish..."

This is pretty wordy, but structurally it's no different than the phrase "politicians decided to postpone the plan." Aside from the opening modifier, there's only one clause (subject + verb) before the -ing modifier ("proposing..."), and that -ing modifier logically modifies the clause right before it.

The same is true in choice (C): the -ing modifier logically modifies the clause right before it, and the meaning is clear enough.

Unfortunately, there isn't a single set of clear and simple rules governing this sort of thing. Sometimes, if you try too hard to invent/memorize/apply rules, you'll miss opportunities to think logically and precisely about the meaning of the sentence -- and that's the thing that matters most.

I hope that helps!

sayantanc2k
Thanks for the broad explanation. I've a little query in your creative example.

It seems that the highlighted part is in list of verb. So, shouldn't it have a COMMA before AND?



We don't have a COMMA before AND in the following example!
https://gmatclub.com/forum/australian-e ... ml#p159993
The example with link is something like ''THAT x and THAT y'' (No COMMA before 2nd THAT)
How can we take decision here in this case?
Thanks__

Hi Experts,
In correct choice C, if we don't put any COMMA before ''and'' then it looks like ''dense regions and more slowly''. Here ''and'' is the connector, right? Shouldn't it make parallel the right part (more slowly) and left part (dense regions) of ''and''?

I know that Punctuation (COMMA) is not tested in GMAT, but without COMMA before 'and' it looks poor, specially in this SC.
It seems that ''dense regions'' is a modifier of ''cold'. So, I think, ''dense regions'' should be separated by COMMA in both side.

GMAT tends to use fewer commas than what we normally do. Let it go and use logic to see what makes sense. Every question has a best option and your job is to look for that.

Hello TheUltimateWinner,

We hope this finds you well.

To answer your query, the comma before "dense" is just used to link the adjectives "cold" and "dense", so even if it looks a bit off, the parallelism in Option C is perfectly fine.

We hope this helps.
All the best!
Experts' Global Team

ExpertsGlobal5
So, what is the role of 'dense regions'? Is it modifier of 'cold' or something else?

KarishmaB
Hello mam,
if we don't separate 'dense regions' from 'and' then it's our job to make a parallelism before and after of 'and'. Am I missing anything here? Sorry to bother you!

When we use multiple adjectives before a noun, we don't necessarily use 'and.'

With cumulative adjectives, we don't use comma.
e.g. It is a brave new world.
The 'new world' is brave.

With coordinate adjectives, we use either comma or 'and.'
Get me a shiny, colourful dress.
Get me a shiny and colourful dress.
Get me a colourful and shiny dress.

So 'most rapidly through cold, dense regions' makes perfect sense. It describes the region as cold and dense. An 'and' after that needn't be a part of this list at all. Also, though the Oxford comma has great acceptability today, its use is debatable. It removes ambiguity sometimes and at others, creates it. So context is all important.

... traveling most rapidly through cold, dense regions and more slowly through hotter rocks.
shows that the elements being joined together are the underlined. They are parallel (adverbs + prepositional phrases).

When the coordinating conjunction joins two independent clauses, we use a comma before the conjunction. But here it is not joining clauses.
When 'and' joins two subjects or objects or verbs etc, we do not use a comma.
... and there is enough debate on how best to use commas.