Photovoltaic cells are made of two thin layers of material, one of the

Photovoltaic cells are made of two thin layers of material, one of them being a semiconducting material such as silicon, the other a metal such as aluminum or silver.

(A) 'one of them being' a semiconducting material such as silicon, the other a metal such as aluminum or silver--- One of them being is wordy and superfluous— poor in style. -- wrong


(B) 'one of them being' a semiconducting material such as silicon, the other being a metal like aluminum or silver --One of them being is wordy and superfluous 2. 'Like' cannot be used for giving examples. Wrong

(C) one of a semiconducting material such as silicon, the other of a metal such as aluminum or silver ---The correct choice

(D) the first of the layers a semiconducting material such as silicon, the other layer a metal such as aluminum or silver -- Classification as the first layer, etc. is not part of the intention. --- Wrong

(E) the first silicon, a semiconducting material, the other silver or aluminum, both metals --- Both cannot modify the singular metal. – Wrong
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When a list is made up of clearly independent items, "and" is generally used.

For example:

I saw a dog, a cat, and a mouse walking together.

In that example, "dog," "cat," and "mouse" are independent items that name what "I saw."

However, in certain cases, "and" can be omitted for stylistic or other reasons.

Let's consider the sentence version created via the use of choice (C).

Photovoltaic cells are made of two thin layers of material, one of a semiconducting material such as silicon, the other of a metal such as aluminum or silver.

Notice that the two modifiers that follow "two thin layers of material" basically repeat "two thin layers of material." So, they are not items in a list that work together. Rather, they act as something along the lines of appositives that appear in sequence to rename what has preceded them.

Thus, the writer may make the stylistic choice to omit "and" in this case.

Notice also that none of the choices include "and." So, for the purposes of answering the question, even if you didn't know that "and" can be omitted from a list in certain cases, you could confidently choose (C) as the best of the choices.

GMAT Sentence Correction questions often use uncommonly used structures, such as the list without "and" seen here, partly for the purpose of confusing test-takers and, most likely, because Sentence Correction question writers are language experts who likely enjoy playing around with such structures.
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Tricky question.

And B are out since one of them is wordy - we have a much concise choice in C.
D is too wordy and adds classification which is unnecessary.

E is wrong because both is modifying a single preceding noun.

Hi Daagh.

I could get why other options beside C are incorrect. But while reading option C, I found it out to be a run on sentence. Would appreciate if you could throw some light.

Thanks,

VeritasKarishma GMATNinja GMATGuruNY egmat mikemcgarry
Can you please explain this question ? Specially option C and D ?

My question is, why is there no requirement to use 'and'

The stuff after the first comma just serves to modify "two thin layers of material". There is no need to use a conjunction with such comma-separated modifying info, as you can see in this example (stolen from this post):

"Jen, the second runner to cross the finish line, collapsed in a heap of exhaustion and decided to give up all forms of running forever."

The part in bold ("the second runner to cross the finish line") is just some extra info modifying "Jen". That info is separated from the rest of the sentence with commas, and we don't need a conjunction to do so.

I hope that helps!
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Can you please tell me if the below explanation is OK ?

The intention of the sentence is to express a fact about the photovoltaic cells.

Facts are preferably written in simple present tense. The usage of being is not preferred.
a) doesn't maintain parallelism. one being semiconductor .... , the other a metal .....

b) being is used in the sentence. This is not preferred to represent a fact.
To cite examples, such as is preferred over like.
We can keep this option but we are going to search for something better .


c) because the two layers appears at the end of the main clause, and the modifiers ''one ...., other ....'' both must refer to the layer.

d) Since there are only 2 layers. The usage of ' one ....., other ....' is preferred.
The usage of the first of the layers suggest that in reality there are a lot of layers.
e) the usage of first to represent one of the 2 layers is not preferred.
This sentence is saying that the two layers will be particular type of semiconductor material / a particular type of metal. Whereas the intention of the sentence is to say that the two layers will be a semiconductor / a metal.
modifier ' both metals' is trying to modify a single metal ' silver or aluminium'. This is awkward.

"Jen, the second runner to cross the finish line, collapsed in a heap of exhaustion and decided to give up all forms of running forever."
In above example, only one modifier is present. What if two modifiers were there as they are present in main SC problem here.
Symbolically,

Clause, modifier, modifier.

What I think "and" is necessary here. I do agree that C is best out of given choice. That could be reason for winning C.

Sometime it is also maintained that two modifiers can be stacked in tandem with any conjunction.
She is beautiful, intelligent girl.
Here is comma is sufficient to keep two modifiers adjacent. No conjunction is need.

Please clarify this point whether we can put two modifiers with comma only and no conjunction is necessary.

VeritasKarishma GMATNinja
What's wrong with the use of "being" in option A and B ?
I eliminated B due to use of "like".
Please clarify both options.

'being' is used for a temporary state only. One of them is not 'being' a semiconductor material, it 'is' a semiconductor material.

Check this post: https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2014/1 ... s-part-ii/

Yes, to give examples it is better to use 'such as' (though it depends on what the other options are).

VeritasKarishma daagh

Can you let me know if my interpretation of the ellipsis in (C) is right? Please

one of a semiconducting material such as silicon, the other of a metal such as aluminum or silver:

one layer made of a semi......, the other layer made of a metal.....

VeritasKarishma

I READ THE COMPLETE DISCUSSION. hOWEVER, STILL CAN'T FIGURE OUT WHY OPTION D& E ARE incorrect

Please help

Here's the official explanation provided by the GMAC for this question:

The sentence is intended to describe the two types of materials that each of the two layers of solar cells is made of. It gives examples of each of those two types of materials. Neither layer is identical with the material of which it is made, but the given sentence errs in identifying the layer and the material. In giving examples of each of the two types of material, the idiomatic construction such as is correctly used.

Option A: This answer choice incorrectly identifies the semiconductor layers with the types of materials of which they are made. The inclusion of being is unnecessary.

Option B: This answer choice errs in identifying the semiconductor layers with the types of materials of which they are made. The inclusion of being is unnecessary. Also, such as and like can each be correctly used to give an example of a type of material. However, it would be rhetorically better to use the same word or phrase in both cases here.

Option C: Correct. The phrase one of them being a semiconducting material correctly implies that the layer is not identical with the material of which it is made. The phrase the other of a metal is similar and parallel in structure. The idiomatic such as is correctly used to introduce examples of a class.

Option D: This answer choice identifies the layers with the types of materials of which they are made, whereas the first part of the given sentence distinguishes the layers from the materials. This discrepancy would render the sentence less coherent. In addition, the wording is unnecessarily verbose, since the context already clearly indicates that the two layers are being described. However, the idiomatic such as is correctly used to introduce examples of a class.

Option E: The first part of the given sentence distinguishes the layers from the materials, whereas this answer choice identifies the layers with materials. This discrepancy would render the sentence as a whole less coherent.

The correct answer is C.

Please note that I'm not the author of this explanation. I'm just posting it here since I believe it can help the community.

Photovoltaic cells are made of two thin layers of material, one of them being a semiconducting material such as silicon, the other a metal such as aluminum or silver.


(C) one of a semiconducting material such as silicon, the other of a metal such as aluminum or silver ---The correct choice

GMATNinja How does the example, you have given for the use of Modifier in between, relate to this pattern of Modifier, Modifier. Please can you clarify a bit more on this usage.

if we focus on parallelism, we are fine
in choice A, being can not be parallel with no being
in choice B, such as and like are not parallel.
in choice D, "the first of the layers " is not parallel with "other layer". I think " the second of the layer" or "the other of the layer" could be parallel to "the first of the layers"
in choice E, " a semiconducting material" is not parallel with " both metals"

Photovoltaic cells are made of two thin layers of material, one of them being a semiconducting material such as silicon, the other a metal such as aluminum or silver.


(A) one of them being a semiconducting material such as silicon, the other a metal such as aluminum or silver

-- the use of 'being' is incorrect here.

(B) one of them being a semiconducting material such as silicon, the other being a metal like aluminum or silver

-- the use of 'being' is incorrect here. 'like' can't be used to describe characteristics.

(C) one of a semiconducting material such as silicon, the other of a metal such as aluminum or silver

-- Looks good. Keep

(D) the first of the layers a semiconducting material such as silicon, the other layer a metal such as aluminum or silver

-- 'the first of the layers' sounds as if there are many layers.

(E) the first silicon, a semiconducting material, the other silver or aluminum, both metals

-- Parallelism issue.

Answer is C.
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Unfortunately, most of the explanations, even those of experts, have not addressed the burning question of many students-

why is there no 'and' in between the two modifiers in C?
Also, how should we infer - 'one of a semiconducting'

I understand that we have to accept OA as the correct answer but I think we need a bit more than just "looks good because OA says so, and hence let's keep it" approach.
I may be wrong but I see the urgent requirement of an 'and' in option C. Experts, please elaborate on these points.

BINGO!! Thanks MartyTargetTestPrep! Literally, thanking you a ton. This is what I was exactly looking for.

So basically, when we get a noun, let's say, and some items in a list that explains the noun in some way and that are not exactly "different" from each other, we can choose to omit 'and'.

Thanks, sir for this ultra simplistic explanation! This is what we were dying for!