An effect of the Pleistocene Ice Age that is difficult to observe visu

Question

Project SC Butler: Sentence Correction (SC1) 
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An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically being that there was a massive transfer of water from the oceans to the land during the glacial periods.

A) An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically being that there was a massive transfer of water from the oceans to the land during the glacial periods.

B) A massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age difficult to observe visually but is quite predictable if one thinks about it logically.

C) That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

D) An effect of the Pleistocene Ice Age, that is difficult to observe visually but quite predictable if one thinks about it logically, is there was a massive transfer of water from the oceans to the land during the glacial periods

E) Difficult to observe visually but quite predictable if one thinks about it logically, that there was a massive transfer of water from the oceans to the land during the glacial periods, is an effect of the Pleistocene Ice Age.

generis · Accepted Answer

OFFICIAL EXPLANATION

Project SC Butler: Sentence Correction (SC1)

THE PROMPT  
 
• The sentence describes an effect of the Pleistocene Ice Age. 
What was this effect? 
Presumably, cold temperatures during an ice age froze water, built up glaciers and drained oceans.
The result was a massive transfer of water from the oceans to the land.

THE OPTIONS  
 
• Missing Verb - Fragment
→  being  is not a verb. The subject of the main clause,  an effect , is not paired with any working verb. The sentence is a fragment. 
ELIMINATE A

• the adjective phrase used to describe  an effect  (it is difficult to observe but logical and predictable) contains a strange IS that seems to come out of nowhere..

→ Either (1) eliminate the  is  after  but,  or (2) add  that is  after  Ice Age  to fix the strange "is" that seems to come from nowhere.

#1, Correct but somewhat abrupt :  A massive transfer of water from the oceans to the land ... is an effect of the Pleistocene Ice Age difficult to observe visually but quite predictable if one thinks about it logically. 
-- in that sentence, the words  difficult  and  predictable  are adjectives that derive from reduced relative clauses.** (see footnote below)

#2, Correct, better diction than #1, and creates sensible context for the repeated IS :
 A massive transfer of water from the oceans to the land ... is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

We need one structure or the other, but we have neither. 
That is, the  is  after but requires a preceding  that is  to create a sensible descriptor that comports with good diction. Alternatively, the word  is  after  but  could be eliminated. 
As it stands, this sentence is strange, confusing, and messy.
ELIMINATE B

• Correct. Although starting sentences with the word  that  is fairly rare, doing so is correct.
→ In this context and others,  that  = "the fact that."
→ For an  official question    in which a that-clause leads off the sentence, click on  this link, here .

•  That  can refer to a fairly distant noun. 
→ Let's reframe this Modifier Touch Rule. Let's call it a guideline.

→ Some of you have been taught that  which  and  that  always modify the immediately preceding noun and/or that those words can never be somewhat distant from their noun.
Wrong.

→ that refers to  effect,   not  to  Ice Age .
The construction is perfectly acceptable.
Why? Because two essential modifiers cannot both be placed right next to the noun.
We have two essential modifiers of the noun "effect": 
(1)  of the Pleistocene Ice Age , and
(2)  that is difficult to observe visually but is quite predictable if one thinks about it logically .

One of those modifiers must be placed before the other.
Prepositional modifiers cannot be placed anywhere else. (The prepositional modifier starts with  of the. )
So two modifiers are placed one after the other. The  that  modifier follows the prepositional modifier.

See Notes, below, for official examples in which  that  does not modify the immediately preceding noun and in which  that  is a bit distant from its noun.

• The sentence, rewritten:
 An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it   logically is   that there was a massive transfer of water from the oceans to the land during the glacial periods.

In the logical context of the sentence, the  that  clause refers to  effect .
It is not the Pleistocene Ice Age that is difficult to observe visually. (It is  impossible  to observe that ice age.)
 That  refers to effect. The effect under discussion is a massive transfer of water from oceans to land. 
This sentence is fine.
KEEP

• unless absolutely necessary, such as when a short phrase intervenes, the essential modifier  that  should  not  be set off by commas
→ As of 2021,  that  and  which  are not interchangeable on the GMAT.
This situation may change. For now, the distinction holds. See the footnote for more information.**

→ Be careful. In British English,  which  and  that  are interchangeable. 
In particular, in B.E., the word  which  can be used to introduce essential information and need not be flanked by commas—not so in SWE and not so on the GMAT.

In SWE and on the GMAT
→  which  is a nonessential modifier that introduces dispensable information and is set off by commas
→  that  is an essential modifier that introduces indispensable information and is not set off by commas

• the subject complement (the thing on the other side of the linking verb  is ) should be an adjective; a noun, noun clause, or noun-like clause; or an adverb of time, location, or direction. See footnote for more on subject complements.**

The subject complement is the clause   there  was a massive transfer of water from the oceans to the land during the glacial periods. 
→  there was a massive transfer  is not an adjective, noun, or special adverb and cannot function as the subject complement of  an effect 
→   that  there was a massive transfer of water from ocean to land  is a  noun clause (also known as a substantive clause, which you can read about by clicking  here )  and thus can function properly as a subject complement.
ELIMINATE D

• Introductory modifier is questionable
→  Difficult to observe . . .  is really a description of "an effect of the Pleistocene Ice Age."
We could argue that "that there was a massive transfer of water" IS the effect. 
At best, the construction is confusing.
→ The modifier issue is a tough call.

• do not unnecessarily place a comma between a subject and its verb
→ remove the comma after  periods,  because the subject    that there was a massive transfer of water  should not be separated from its verb,  is,  by a comma. 
→ If we inverted the sentence, we would not place a comma between subject and verb.
→ Inverted sentence with a comma, wrong: An effect of the Pleistocene Ice Age IS   ,     that there was a massive transfer of water.
Do not separate the subject from its verb.

Compare. This sentence is not as good as option C.
ELIMINATE E

The correct answer is C.

NOTES

•  Can THAT refer to a faraway noun?     Absolutely.

Some of you are taught that there are  no exceptions  to the Modifier Touch Rule.
The latter is not a rule in the way that, say, subject/verb agreement is a rule.

The latter is a guideline.
This  guideline  states that a modifier should be as close as possible to the noun that it modifies.

I have no idea how that guideline turned into a rigid insistence that words such as  which  and  that , or participle adjectives, must modify the immediately preceding word. That belief is inaccurate.

Yes, for the most part, the closer noun modifiers are to their nouns, the better.
Not always.

PyjamaScientist  , I hope that others' explanations, this explanation, and the examples I provide put your question to rest.
I am sure that quite a few other people had the same question.
Let's hope that everyone who needs to do so reads the material.

→ THAT - can modify a noun without being right next to that noun

Both  that  and  which  and other kinds of noun modifiers can modify the   head noun   in a noun phrase such as   effect  of the Pleistocene Ice Age.

In case you do not wish to view official questions in which  that  modifies a slightly faraway noun, the first example is my own.

(1)  The  underground corridor system  at Harvard Law School  that was built to protect students from bitter winter cold  routinely confounded my sense of direction; during my first year, I finally just stayed close to section mates who knew where our next class was located.

That  refers to an underground corridor system. This much I promise: Harvard Law School was not built to protect students from bitter winter cold.
 
Again, we have two essential modifiers.
At which law school are the underground corridors? 
Stanford Law and Yale Law do not have a system of underground corridors through which students can get from class to class in different buildings without having to go outside.
(Well, at least not any that I saw when I visited those schools.)
In other words, those corridors are at  Harvard  Law School. (And yes, I got lost constantly.)

Why were and are students running around beneath the buildings of a law school in corridors?
What is distinctive about this system of corridors? 
Answer: The system of corridors was built to protect students from brutally cold New England winters.
 That  refers to to a slightly distant noun.

(2) You can read an official question example in which  that  modifies a slightly faraway noun if you  click here .
That question was published in every official guide from 2011 to 2020.

(3) Another official question example in which  that  is ten words away from its noun can be found by  clicking here .
(This question was in the Official Guide  Diagnostic  test from 2012 to 2020.)

Numbers 2 and 3 are but two examples that I found by flipping through one OG. 
I remembered keywords and knew what I was looking for. 
Long prepositional or adjectival phrases "bump" the words  that  and  which  farther toward the end of the sentence, but the latter two modifiers are still allowed to modify their nouns.

• Thoughts on tone in a couple of posts
I understand that SC can be frustrating.
Language is not math.

But language is learnable.

Start reading U.S. based high end journals and newspapers. Read fiction. 
Read every single day for at least 20 minutes. That suggestion applies to native speakers, too.
If you have more time, read for a longer period of time. Read in two 20- or 30-minute stretches. 
Wanna beat this test? Channel some of your energy into reading.
Find a way to get engaged.

Kvetching is not going to beat this test.
Arguing with the correct answer is not going to help you beat this test.

And I want all of you to beat this test.

COMMENTS

To all who helped and engaged constructively on the thread: thank you.

Kudos to those who posted correct answers or who helped.

**
 Option B, adjectives derived from reduced relative clauses .

From above, this sentence is
 #1, correct but somewhat abrupt : A massive transfer of water from the oceans to the land ... is an effect of the Pleistocene Ice Age  difficult  to observe visually but quite  predictable  if one thinks about it logically.
→ in that sentence, the words  difficult  and  predictable  are adjectives that derive from "reduced relative clauses."

In this sentence, the original relative clauses are intact:  A massive transfer of water . . . is an effect . . . THAT IS DIFFICULT to observe visually but THAT IS quite PREDICTABLE if one thinks about it logically.

To reduce this kind of relative clause, 
(1) remove the relative pronoun ( that ), 
(2) remove the to be verb ( is ), and 
(3) keep the adjective.
→ Again, the sentence now contains "reduced relative clauses":  A massive transfer of water . . . is an event  difficult  to observe but quite  predictable  if one thinks about it logically.

THAT/WHICH

Some experts believe that GMAC no longer maintains a distinction between  which  and  that. 
GMAC may well be relaxing its rules about this distinction, but GMAC has not abandoned it.
In Official Guides from 2020, 2021, and 2022, GMAC still tested the issue.

SPOILER ALERT  In OG 2020, SC #824 explicitly tested the which/that distinction.
OGs 2021 and 2022 both contain that question.
The recent official question that tests this distinction can be found by clicking  here .

Subject complement : adjective, noun/noun clause, special adverb

Is  is a linking verb similar to an "equals" sign.
Is links a subject to its subject complement. A subject complement is something that describes the subject.
Subject complements can be 
→ adjectives:  Rebekah is  tall  .
→ nouns or noun clauses ("what constitutes"):  Misinformation is  what constitutes the biggest threat to this country.  
→ adverbs of time, location, or direction:  The meeting was  yesterday.

Subject complements cannot begin with existential  there .
→  Wrong : According to a recent book by two Pulitzer Prize winners, the ugly truth about January 6, 2021 is there was very nearly a coup. 
→  Correct : According to a recent book by two Pulitzer Prize winners, the ugly truth about January 6, 2021 is   that  there was very nearly a coup,  about which military leaders were worried.
The italicized part is a noun clause. That noun clause begins with  that . Not  there . Noun clauses do not begin with  there.

sumitkrocks · Answer

A) An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically being that there was a massive transfer of water from the oceans to the land during the glacial periods.

An effect of the Pleistocene Ice Age   that is difficult to observe visually but is quite predictable if one thinks about it logically   being that there was a massive transfer of water from the oceans to the land during the glacial periods.

"It" refers to An effect or Pleistocene Ice Age ??
Being is wrongly used 
That clause, jumping over the prepositional noun phrase, is modifying an effect

B) A massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age difficult to observe visually but is quite predictable if one thinks about it logically.

Ice age difficult to observe ...and "massive...." is quite changes meaning

C)  That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

Subject : That there was a massive transfer of water from the oceans to the land during the glacial periods
that refers to effect and sentence is parallel

Correct choice IMO with No ambiguous Pronouns

D)  An effect of the Pleistocene Ice Age, that is difficult to observe visually but quite predictable if one thinks about it logically, i s there was a massive transfer of water from the oceans to the land during the glacial periods
The introductory modifier is a dangling modifier with no assigned subject -Eliminate
"That" clause enclosed b/w commas is also not structurally right 
 
E)  Difficult to observe visually but quite predictable if one thinks about it logically, that there was a massive transfer of water from the oceans to the land during the glacial periods,  is an effect of the Pleistocene Ice Age.
The introductory modifier is a dangling modifier with no assigned subject -Eliminate
"That" clause enclosed b/w commas is also not structurally right

zhanbo · Answer

I Chose  (C) .

(A) In reading (A), I first took issue with the location of "that is difficult to observe visually..." because it appears to modify "the Pleistocene Ice Age": There might be multiple said Ice Ages, and the author uses a restrictive relative clause to zero in on the Pleistocene Ice Age that is difficult to observe. It occurred to me later that all but (E) exhibit such issue.

I ended up eliminating (A) because of "being that...". It is not a sentence.

(B) "difficult to observe visually" is not parallel with "is quite predictable". One fix is to remove "is".

(C) Not an instant hit. There are multiple issues in (C). 
(1) As discussed in (A), "that is difficult to observe visually..." seems to modify "the Pleistocene Ice Age"
(2) "predictable  if one thinks about it logically " is wordy. Anything "predictable" inherently assume that "one thinks about it logically". Simply using "predictable" is better. 
(3) That ... is an effect" can be better organized to be "the effect that ... is". 
This sentence can thus read:
  Better sentence:   The effect that there was a massive transfer of water from the oceans to the land during the glacial periods of the Pleistocene Ice Age is difficult to observe visually but is quite predictable.
Hold (C) and check whether (D) or (E) is better.

(D) "that", placed after a comma, should be "which". 
(E) The subject "that there was ..." should be followed by "is an effect" without the comma in between.

(D) or (E) contains mistakes. (C) is the best answer.

Anuragsharma93 · Answer

IMO C

Lot of prepositions and meaning issues... this is how i eliminated the other answer choices.

An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically being that there was a massive transfer of water from the oceans to the land during the glacial periods.

A) An effect of the Pleistocene Ice Age  that is difficult to observe  visually but is quite predictable if one thinks about it logically  being that there was  a massive transfer of water from the oceans to the land during the glacial periods. - The structure is that______ that not Being That ____ also the meaning of the sentence is not correct.

B) A massive transfer of water from the oceans to the land during the glacial periods is an effect of the  Pleistocene Ice Age difficult  to observe visually but is quite predictable if one thinks about it logically. - Meaning error - we need to words Which is difficult. Also there is tense error.

C) That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

IMHO, I don't agree with any of the answers.

Reading the entire sentence gives a feeling that there is no main verb at all in the sentence.

D) An effect of the Pleistocene Ice Age, that is difficult to observe visually but quite predictable if one thinks about it logically,  is there was  a massive transfer of water from the oceans to the land during the glacial periods- Redundant

E) Difficult to observe visually but quite predictable if one thinks about it logically,  that there  was a massive transfer of water from the oceans to the land during the glacial periods, is an effect of the Pleistocene Ice Age. -- The subject of the sentence should follow the innitial comma and if we remove the phrase between the two commas the sentence doesnt make sense. Difficult to observe visually .....is an effect of Pleistocene ice age..

PyjamaScientist · Answer

IanStewart

I am really having serious doubts on how my fellow peeps have been marking option C as the right answer. And so, I dearly wait for the OE when OA releases.

Let's analyze option C, 
 That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

Shortening it-
 That  there was a massive transfer  is  an  effect of Pleistocene Ice Age that is   difficult to observe but  is  predictable if one thinks about it.

First part  is okay, but the  second part   does not make sense to me.  that is difficult...  is modifying the Ice Age. I don't think the author meant to say that the Ice age was difficult to observe rather the  massive transfer of water .

Option D, except that it uses comma + that, looks more close to the actual meaning.

swim2109 · Answer

IMO C is the answer.

C correctly organizes the sentence by preserving the parallel structure and the meaning.

A) An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically being that there was a massive transfer of water from the oceans to the land during the glacial periods.-------> Being usage jumps at me. Its awkward and wrong

B) A massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age difficult to observe visually but is quite predictable if one thinks about it logically.----> 'is quite predictable' not || to difficult to observe

C) That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

IMHO, I don't agree with any of the answers.

Reading the entire sentence gives a feeling that there is no main verb at all in the sentence.

D) An effect of the Pleistocene Ice Age, that is difficult to observe visually but quite predictable if one thinks about it logically, is there was a massive transfer of water from the oceans to the land during the glacial periods----> meaning altered. In addition, 'is there was a massive' seems wrong as that should be used

E) Difficult to observe visually but quite predictable if one thinks about it logically, that there was a massive transfer of water from the oceans to the land during the glacial periods, is an effect of the Pleistocene Ice Age.---->Whats the subject of is??!

sumitkrocks · Answer

PyjamaScientist  I believe second that, in your analysis of option C, refers to "an effect" not to "the Ice Age"
In some exceptional cases "That" can jump of preceding prepositional phrase to modify a slightly far noun..

Breakdown the intended meaning of the author :-
 
Pleistocene Ice Age is a period with certain whether conditions. 
A period that resulted in a certain effect difficult to observe visually but quite predictable if one thinks about the effect logically. 
Effect was a massive transfer of water from the oceans to the land during the glacial periods.

Hope it helps

kantapong · Answer

A is wrong because there is no main verbs (main verb is supposed to be "being" -> "is")
E is wrong because it is ambiguous (what it refers to)
B is quite predictable is parallel to a massive transfer (distorted meaning: what is predictable should be effect of Ice Age)

C and D are quite close 
C: That there was ... is an effect ... that is difficult to observe but is quite predictable
D: An effect ..., that is difficult to observe but quite predictable, is there was a massive transfer ...

I cannot decide between the two, but I go with D for now because (comma) makes the sentence clearer (I guess?)

IanStewart · Answer

If you read a sentence like this:

Bita picked up the glass of water that was on the counter.

the only reasonable way to interpret this sentence is in this way:

Bita picked up {the glass of water} that was on the counter.

Here, "that" is referring back to the meaningful unit before "that", which is "the glass of water". It is not referring to "water" alone (that interpretation would be very strange -- that would mean at one point the water was in a pool on the counter, and then later the water ended up in a glass that Bita picked up).

As sumitkrocks points out above, "that" does not always refer to the immediately preceding word. It can certainly refer back instead to the immediately preceding meaningful grouping of words. And I wouldn't characterize this as "exceptional"; we use "that" in this way all the time, and it's perfectly fine. In this question, it's the unit "effect of the Pleistocene Ice Age" that the word "that" is referring to. That needs to be true, because "effect" is the only word that can be the subject of the word "is" immediately after "that".

walthcapp88 · Answer

I will focus on C and B given that i can see lots of C and i am not convinced.

B) A massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age difficult to observe visually but is quite predictable if one thinks about it logically.

I am not convinced by the initial A > shouldnt be THE?!

C) That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age  that is  difficult to observe visually but is quite predictable if one thinks about it logically.

Is it refered to ice age? or the effect?
-----------

Is it this an official one or not?

Fdambro294 · Answer

IanStewart  wrote an excellent post above discussing when a noun modifier beginning with “that” may refer to the head of a noun phrase (when “that” can jump over certain essential noun modifiers).

With respect to answer (C), the “that” logically refers to the “effect.” In every case, “that” does not have to refer to the immediately preceding noun.

If you think about the sentence in the context of its overall meaning, the modifier following “that” is referring to the entire noun phrase or “an effect of the Pleistocene Age.”

It doesn’t make logical sense to say that a timeline of history is difficult to observe visually. It would be a bit of a stretch to say:

“The Age of the Roman Empire is difficult to observe visually.”

Unless it becomes ambiguous with respect to the object of the prepositional phrase, it’s easier to think of the essential noun modifier following “that” as modifying the entire noun phrase, not just a single word.

Posted from my mobile device

generis · Answer

The official explanation is  here .

sanjitscorps18 · Answer

C) That there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

IMHO, I don't agree with any of the answers.

Reading the entire sentence gives a feeling that there is no main verb at all in the sentence.

Reading the entire sentence gives a feeling that there is no main verb at all in the sentence. Starting with "That", I was wondering how would the sentence transition but it never happened. The sentence is essentially That.....is an effect.....that is.....difficult.......but.....(end of sentence). A simple article "A" instead of "That there was a" would be a useful alternative. However, I just cannot fathom how Option C is the answer, or for that matter any of them. Experts generis IanStewart and others are welcome to comment

IanStewart · Answer

If you rearrange the sentence, putting the second half first, you might see more easily that there is a main verb, "is":

An effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically is that there was a massive transfer of water from the oceans to the land during the glacial periods.

"That" is a versatile word used in all kinds of ways, and in the usage in the original sentence, it introduces an entire clause that will be the subject of the sentence. You won't encounter that usage all that often, but you will on occasion. "That I would need thyme for the dish is something I hadn't planned for", for example, is the same usage in a simpler sentence, and while it sounds overly formal, it's perfectly correct. The original sentence you asked about is overly wordy, but otherwise it seems fine to me grammatically.

edit: I just realized I replied earlier in this thread, also about how this sentence uses the word "that", but the sentence uses "that" twice in different ways. My earlier post was discussing the other "that" in the sentence, which is used to introduce a modifier.

ExpertsGlobal5 · Answer

Dear Friends,

Here is a detailed explanation to this question-

Meaning is crucial to solving this problem: 
Understanding the intended meaning is key to solving this question; the intended meaning of this sentence is that the fact that there was a massive transfer of water from the oceans to the land during the glacial periods is an effect of the Pleistocene Ice Age that is difficult to observe visually but is quite predictable if one thinks about it logically.

Concepts tested here: Grammatical Construction + Verb Forms + Parallelism

• All elements in a list must be parallel.
• Information that is vital to the core meaning of the sentence must not be placed between two commas.

A:  This answer choice fails to form a complete sentence; as "that is difficult", "that...is quite predictable" and "being" are all noun modifiers, there is no active verb to act upon the subject noun phrase "An effect of the Pleistocene Ice Age"; please note that here "being" is a present participle ("verb+ing" - "be + ing" in this sentence).

B:  This answer choice fails to maintain parallelism between the noun modifier "difficult to observe visually" and the active verb phrase "is quite predictable"; please remember, any elements linked by a conjunction ("and" in this sentence) must be parallel.

C:   Correct.  This answer choice acts upon the subject pronoun "That", a placeholder pronoun, with the active verb "is" to form a complete thought, leading to a complete sentence. Further, Option C correctly maintains parallelism between the noun modifiers "is difficult to observe visually" and the active verb phrase "is quite predictable". Additionally, Option C avoids the grammatical construction error seen in Options D and C, as it places no information between commas.

D:  This answer choice incorrectly places information that is crucial to the meaning of the sentence - the fact that the effect is difficult to observe visually but quite predictable if one thinks about it logically - between two commas; please remember, information that is important to the core meaning should not be placed within two commas.

E:  This answer choice incorrectly places information that is crucial to the meaning of the sentence - the fact that there was a massive transfer of water from the oceans to the land during the glacial periods - between two commas; please remember, information that is important to the core meaning should not be placed within two commas.

Hence, C is the best answer choice.

To understand the concept of "Extra Information Between two Commas" on GMAT, you may want to watch the following video (~1 minute):

https://www.youtube.com/watch?v=awY1dV_vETw

All the best!
Experts' Global Team

An effect of the Pleistocene Ice Age that is difficult to observe visu

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