Scientists have recently found evidence that black holes—regions of sp

Dear Friends,

Here is a detailed explanation to this question-

Concepts tested here: Subject-Verb Agreement + Parallelism + Comparison + Grammatical Construction

• Semicolons and the “comma + conjunction” construction are used to link two independent clauses; commas are used to link an independent clause with a dependent one; comma cannot be used to join two independent clauses.
• Any elements linked by a conjunction (“and” in this sentence) must be parallel.
• A comparison must always be made between similar things.

A: This answer choice fails to maintain parallelism between "that the black holes...exist at the core of nearly all galaxies" and "the mass of each black hole is proportional to its host galaxy"; please remember, any elements linked by a conjunction ("and" in this case) must be parallel. Further, Option A incorrectly compares "the mass of each black hole" to "its host galaxy"; please remember, a comparison must always be made between similar things.

B: Correct. This answer choice correctly refers to the plural noun "black holes" with the plural verb "exist". Further Option B maintains parallelism between "that the black holes...exist at the core of nearly all galaxies" and "that the mass of each black hole is proportional to its host galaxy". Additionally, Option B correctly compares "the mass of each black hole" with "that (mass) of its host galaxy". Besides, Option D correctly uses conjunction ("and" in this sentence) to join the dependent clauses "that the black holes...exist at the core of nearly all galaxies" and "that the mass of each black hole is proportional to its host galaxy".

C: This answer choice incorrectly compares "the mass of each black hole" to "its host galaxy"; please remember, a comparison must always be made between similar things. Further, Option C incorrectly uses the "comma + conjunction ("and" in this sentence)" construction to join the dependent clauses "that the black holes...exist at the core of nearly all galaxies" and "that the mass of each black hole is proportional to its host galaxy"; please remember, conjunction is used to join two parallel dependent clauses, and the "comma + conjunction" construction is used to join independent and dependent clauses.

D: This answer choice incorrectly refers to the plural noun "black holes" with the singular verb "exists". Further, Option D incorrectly uses the "comma + conjunction ("and" in this sentence)" construction to join the dependent clauses "that the black holes...exist at the core of nearly all galaxies" and "that the mass of each black hole is proportional to its host galaxy"; please remember, conjunction is used to join two parallel dependent clauses, and the "comma + conjunction" construction is used to join independent and dependent clauses.

E: This answer choice incorrectly refers to the plural noun "black hole" with the singular verb "exists". Further, Option E fails to maintain parallelism between "that the black holes...exist at the core of nearly all galaxies" and "the mass of each black hole is proportional to its host galaxy"; please remember, any elements linked by a conjunction ("and" in this case) must be parallel.

Hence, B is the best answer choice.

All the best!
Experts' Global Team

I suggest a split pattern approach

the core structure should be: Scientists found evidence that [clause 1] and that [clause 2]
or
Scientists found evidence that [clause 1] and [clause 2]
(Both are acceptable)

[Clause 1]: black holes, .....[modifier], probably exist at the core of nearly all galaxies => plural Subject go with plural Verb => We eliminate D & E
[Clause 2]: the mass of each black hole is proportional to ........

There is a very clear patter
A - B - C with "Exist at the core of nearly all galaxies......."
D - E with "Exists at the core of ......"

From [Clause 1], as "black holes" is plural subject => need plural verb => eliminate D - E immediately as "exists" is in the singular form.

Now the case is
(A) exist at the core of nearly all galaxies and the mass of each black hole is proportional to
(B) .......................(like A)...................... and that the mass of each black hole is proportional to that of
(C) .......................(like A)....................., and that the mass of each black hole is proportional to

The 2rd pattern to split will be:
A - C: exist at the core of nearly all galaxies(,) and (that) the mass of each black hole is proportional to
B: ...................................................................................................is proportional to that of

At this step I will question the difference between A-C and B.
When we look closer to the [Clause 2], it is clear that "the mass of each black hole" should be proportional to the mass of something else, as A proportional to B only if A and B are equally sign.

In A - C, the mass of each black hole is proportional to its host galaxy => although I'm not an astrologer, and don't know what is the "mass", it don't make sense together

While in B, the mass of each black hole is proportional to that of (that of=the mass of) its host galaxy

==> at the end, eliminate A - C,

B is the only left one.

Basically I was confused between B and C I rejected B because of usage of That of can anyone explain how usage of that of is correct in B and why C is wrong

Hello Everyone!

This is a great example of a GMAT question that focuses on parallelism and subject-verb agreement! Let's start by taking a quick look at the original question, and highlighting any major differences between the options in orange:

Scientists have recently found evidence that black holes—regions of space in which matter is so concentrated and the pull of gravity so powerful that nothing, not even light, can emerge from them—probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.

(A) exist at the core of nearly all galaxies and the mass of each black hole is proportional to
(B) exist at the core of nearly all galaxies and that the mass of each black hole is proportional to that of
(C) exist at the core of nearly all galaxies, and that the mass of each black hole is proportional to
(D) exists at the core of nearly all galaxies, and that the mass of each black hole is proportional to that of
(E) exists at the core of nearly all galaxies and the mass of each black hole is proportional to that of

After taking a quick glance over the options, 2 major differences jumped out:

1. exist vs. exists (subject-verb agreement)
2. to vs. to that of (parallelism)

Let's start with #1 on our list: subject-verb agreement. If we look at the entire sentence, we should be able to identify the subject that matches up with the verb "exist/exists" pretty quickly:

Scientists have recently found evidence that black holes—regions of space in which matter is so concentrated and the pull of gravity so powerful that nothing, not even light, can emerge from them—probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.

Since the subject "black holes" is plural, we need to make sure the verb we use is also plural:

(A) exist at the core of nearly all galaxies and the mass of each black hole is proportional to
(B) exist at the core of nearly all galaxies and that the mass of each black hole is proportional to that of
(C) exist at the core of nearly all galaxies, and that the mass of each black hole is proportional to
(D) exists at the core of nearly all galaxies, and that the mass of each black hole is proportional to that of
(E) exists at the core of nearly all galaxies and the mass of each black hole is proportional to that of

We can eliminate options D & E because the singular verb "exists" doesn't match the plural subject "black holes." Pretty easy, right?

Now let's tackle #2 on our list: parallelism. This sentence is comparing two items, and we need to make sure that they are parallel in type. To make this easier to spot, we'll add the rest of the comparison to each option for you. Here's how they break down:

(A) exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.

This is INCORRECT because it's comparing mass to galaxy, which aren't the same thing at all!

(B) exist at the core of nearly all galaxies and that the mass of each black hole is proportional to that of its host galaxy.

This is CORRECT! It's clear that by adding in the phrase "that of," we're now comparing the mass of each black hole to the mass of its host galaxy, which is parallel.

(C) exist at the core of nearly all galaxies, and that the mass of each black hole is proportional to its host galaxy.

This is INCORRECT because it's trying to compare mass to galaxies, which aren't parallel.


There you have it - option B is the correct choice! It uses proper parallel structure to compare two items, and it doesn't have any subject-verb agreement issues!


Don't study for the GMAT. Train for it.

C is wrong because it compares "mass of black hole" to "the parent galaxy" (instead of comparing to the parent galaxy's mass). Invalid comparison.

B all the way!

Two concepts are tested here.

1) SV agreement
2) Comparison

Subject " Black Holes " plural needs plural verb

D and E gone.

Comparison needs to be between mass of the BH and mass of host galaxy.

B uses both these concepts correctly.

Time taken : 30 sec

The sentence says that scientists have recently found evidence for two things.

The black holes probably exist at the core of nearly all galaxies
The mass of each black hole is proportional to its host galaxy
Please note that the sentence also provides a lot of information about black holes within two dashes. You can read the idea between the dashes. However, the more important thing is that when you start reading after the closing dash, read as if the dashes and everything contained within the dashes weren’t there. In other words, you shouldn’t get lost in the deluge of information in the dashes and should be able to connect the part of the sentence that appears after the dashes to the part before the dashes.

There are two problems with this sentence:

“That” is missing after ‘and’. To make it clear that the evidence suggests “that the mass of each…”, we need to place ‘that’ before “the mass of each…”. Without ‘that’, it may seem like another independent clause having nothing to do with evidence.
The second problem is with the meaning. It doesn’t make sense to say that the mass of X is proportional to a galaxy. Probably, we mean to say that the mass of X is proportional to the mass of a galaxy. Therefore, the second part of the sentence should be modified to say “proportional to the mass of its host galaxy”. Please note that when we are evaluating the options, we need to be flexible i.e. even though it seems to be “proportional to the mass of its host galaxy”, it may eventually turn out to be “proportional to the size of its host galaxy”.

Think about (C) in comparison to (B).

In (B), we get the following construction: "the mass of each black hole is proportional to that of its host galaxy."

Here, it's crystal clear that "that" is a stand-in for mass, and we're comparing the mass of a black hole to the mass of the host galaxy. Makes sense.

In (C), we get: "the mass of each black hole is proportional to its host galaxy."

Now we have to play mind-reader. Did the writer mean to compare the mass of black hole to the host galaxy itself? Did the writer mean to compare the mass of one to the mass of the other, but just left off the second "mass," assuming we'd be able to figure that out?

The first interpretation is illogical. And even if we want to argue that the second interpretation is possible, there's no real clue to indicate that this was the intent, leaving it to the reader to guess. At best, it's confusing.

So no need to agonize. (B) is clear. (C) is not. Clear is better, so (B) is our answer. Simple as that.

I hope that helps!

Remove the parenthetical stuff to get a clear idea of Subject-Verb agreement
Scientists have recently found evidence that black holes—regions of space in which matter is so concentrated and the pull of gravity so powerful that nothing, not even light, can emerge from them—probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.


The sentence now becomes
Scientists have recently found evidence that black holes probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.

"Black holes+exist & that" will be the correct construction with respect to parallelism and SV agreement

D and E are wrong outright

Among A,B,C
A is out Wrong parallelism becauses it is missing "that"
exist at the core of nearly all galaxies and the mass of each black hole is proportional to. needs a "THAT" after "and "for correct parallelism.

C is out
Wrong comparison .. compares mass of the black hole to the galaxy itself
exist at the core of nearly all galaxies, and that the mass of each black hole is proportional to

B is correct
compares mass of the black holes to that of the parent galaxy
(B) exist at the core of nearly all galaxies and that the mass of each black hole is proportional to that of

In general, I don't think it's a good idea to overreact to commas on the GMAT, partly because style experts disagree about comma rules, and partly because the GMAT has better things to worry about. In (C), I don't see any need for the comma, since the two "that" phrases ("that black holes... probably exist" and "that the mass of each black hole is proportional...") are parallel to each other. In this case, it's basically a "list" of two subordinate clauses, so no need for a comma.

But you're very, very unlikely to see an official GMAT question in which the comma is the deciding factor.

I hope this helps!

Masterscorp


The basic concept of using that in two-part sentences.
If Something does two things, those things must be presented parallelly in structure and meaning joined by the introducing connector 'that.' For example. we may say that
<John reported to his wife that he got 800 in GMAT and that it all happened because of her help >
We need the connector that because of the two equally important things.
Rule No 2. If you are reporting only one thing and if the second part is n independent event not related to the first, then the golden rule is that there must be a comma before the word 'and' to forewarn that a new clause is about to begin
In my example, we might re-write the whole thing if we drop the 'that'.
John reported to his wife that he got 800 in GMAT,
and it all happened because of her help. But still one can see the disconnect in that legitimately grammatical clause
In other words, when we write compound sentences with two independent terms, then there must necessarily be a comma before the fanboys conjunction

I fully agree with Masterscorp

I know that this doesn't really answer your question (and somebody else already answered it, anyway)... but here's a video about punctuation on GMAT SC: https://www.youtube.com/watch?v=JLAJ_drP8UM.

The punchline is basically that there's no real reason to worry much about the exact rules surrounding dashes, partly because English-language editors (I used to be one!) and style experts don't remotely agree on the best ways to use dashes. If you pick up a bunch of the world's best publications written in English, you'll see a whole bunch of different opinions about how to use dashes correctly -- and about whether they should be used at all. Some editors hate them.

And on the GMAT? You'll see dashes, but they're never really the deciding factor, partly because I don't think that the GMAT wants to try to settle a broader debate about dashes. On official questions, there are always more important issues in the sentence, and you can always answer the question without really worrying about whether a dash was the best choice of punctuation.

I hope this helps!

Thanks neetis5 for the awesome reply!

Adi88, there is no black and white "rule" for the case you described. As suggested by neetis5, it's just a matter of clarity: the comma(s) might make for a "smoother reading experience".

Bottom line: if you have two independent clauses, you need the comma+conjunction (or a semicolon). But just because you have a comma+conjunction does NOT necessarily mean you'll need an independent clause on either side! The GMAT is fairly lenient when it comes to comma usage, so you'll want to look for other decision points.

Scientists have recently found evidence that black holes—regions of space in which matter is so concentrated and the pull of gravity so powerful that nothing, not even light, can emerge from them—probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.

(A) exist at the core of nearly all galaxies and the mass of each black hole is proportional to --Incorrect comparison between mass and galaxy

(B) exist at the core of nearly all galaxies and that the mass of each black hole is proportional to that of --Correct

(C) exist at the core of nearly all galaxies, and that the mass of each black hole is proportional to --Same error as in A

(D) exists at the core of nearly all galaxies, and that the mass of each black hole is proportional to that of --SV disagreement

(E) exists at the core of nearly all galaxies and the mass of each black hole is proportional to that of --Same error as in A and D

Scientists have recently found evidence that black holes—regions of space in which matter is so concentrated and the pull of gravity so powerful that nothing, not even light, can emerge from them—probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.

(A) exist at the core of nearly all galaxies and the mass of each black hole is proportional to

(B) exist at the core of nearly all galaxies and that the mass of each black hole is proportional to that of

(C) exist at the core of nearly all galaxies, and that the mass of each black hole is proportional to

(D) exists at the core of nearly all galaxies, and that the mass of each black hole is proportional to that of

(E) exists at the core of nearly all galaxies and the mass of each black hole is proportional to that of

Split #1: The first verb in our choice refers to the plural noun "black holes". Hence, the verb has to be in plural form as well, which is "exist". Consequently, we can eliminate all answers that start with the singular form "exists" - answers D) and E).

Split #2: The comparison. We compare the mass of each blackhole with that of its host galaxy by saying that there is a proportional relationship between the two. To build a proper comparison we need to use "that of" at the end of the answer choice. By doing that we get "[...] that the mass of each black holo is proportional to that of its host galaxy". This is a correct comparison. As answers A) and C) lack this proper comparison, we can preclude them.

This leaves us with B) as the correct answer. It can also be noted that A) and E) don't maintain parallelism because they lack a "that".

Hope that helps

Hello dave13,


Although this question is not for me, I would be glad to help you out with this.


In this official sentence, the two dashes have been used as a comma pair to enclose some extra description, in this case the description of the black holes.


As far as your choosing Choice D as the correct answer is considered, I would say that Choice D and E are the easiest choices to reject because the SV number agreement error is the easiest to spot.



Hope this helps.
Thanks.
Shraddha

-Three things i observed
1. S-V agreement(black holes - exist/exists)
2. Parallelism(and)
3. Meaning(recent discovery v/s fact)
4. Comparison(Mass of black holes to host galaxy)

Based on S-V agreement D & E are out(plural subject and singular verb). Parallelism and Meaning are interdependent here since parallelism create a different meaning(that Black holes existence is a recent discovery and proportionality of black hole mass to host galaxy is a known fact which is not) which is vague certainly because without knowing about apples one can't say anything about its taste. This becomes easier to understand by hiding the sentence part between two dashes. Lastly, the Comparison just nails things down to one option i.e. B.

Option-(B) Correct.

Hope this is clear enough understanding on my part though i first saw comparison and then realized the meaning of sentence, hence marked B. Definitely, would want to know/see the meaning as early as possible. Trying my best.

Comments and inputs are most welcomed.