D is the correct answer as per my reasoning

Subject is singular ( the chain of retail stores) so it should be its suppliers’
Also the correct construction is not only... but also...

Option D corrects both issues

The chain is singular so their suppliers is Incorrect.



The S-V agreement in both the options is fulfilled but the idiom construction in option B is incorrect.

IMO D.
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Question:
To ensure consistently high quality in its merchandise, the chain of retail stores became involved in every aspect of their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as the profit margins of those suppliers.

Error Analysis:
1) The chain of retail stores is singular. Usage of their is incorrect. (check the bold part in question- its is used to refer the chain of retail stores)
2)correct idiom: not only.. but also..

POE:
A) Incorrect for both the reasons stated in error analysis.
B)Incorrect idiom usage.
C)Corrects the idiom error, but incorrectly uses their to refer to the chain of retail stores.- eliminate
D) Corrects both the errors stated in error analysis.
E)Incorrect for both the reasons stated in error analysis.

IMO: OPTION D

IMO,the correct answer choice is Option D.

The correct usage of "Not only...but also..." boils the answer choices down to Options C and D. In order to tackle the dilemma between "their suppliers" and "its suppliers", one may refer back to the non-underlined part of the question stem wherein its clear that the subject,i.e. "THE CHAIN of retail stores..." clearly indicates that the singular subject(the chain) must take a singular pronoun(its). That rules out Option C.
Although option E does not use the expression of "not only...but also...", it can be eliminated for the incorrect usage of the pronoun.

Hence,Option D is the best answer choice.

Here there are two erros

Subject very the chain .....their
Idiom not only ....but also

Now a and b is having both idiom with a has subject verb as well

C is having error of subject verb the chain ....their

D is fine

E does not maintain the contrast by removing the not only but also

Posted from my mobile device

To ensure consistently high quality in its merchandise, the chain of retail stores became involved in every aspect of their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as the profit margins of those suppliers.


(A) their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as - Pronoun issue - "Their" incorrectly refers to the chain; Not only X but also Y idiom

(B) its suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as - Idiom issue -Not only X but also Y

(C) their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment but also - Pronoun issue - "Their" incorrectly refers to the chain

(D) its suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment but also - Correct

(E) their suppliers’ operations, dictating the number of stitches, the width of the hem in every garment, and - - Pronoun issue - "Their" incorrectly refers to the chain ; changes the meaning -- the original sentence intends to convey that chain dictates not only the number of stitches and the width of the hem in every garment(minute details) but also the profit margins of those suppliers(big things) whereas this options all of them in parallel.

Answer D
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A, C & E - out - all of them use 'their' to point to singular 'Chain' . ( Another hint 'its' is there at the 1st non-underlined dep clause).
B - out - not only..... as well as - is not correct ..... not only..... but also is a very strict idiom.
Hence Ans D
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The first confusion that may arise is between its suppliers and their suppliers. Since the chain of retail stores is singular, hence its supplier will be correct. Moreover it can seen from the first phrase "To ensure consistently high quality in its merchandise". Since it says its merchandise , hence further it should be its suppliers.

Secondly "not only" will be completed with a "but also" phrase.
Hence D is correct.

To ensure consistently high quality in its merchandise, the chain of retail stores became involved in every aspect of their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as the profit margins of those suppliers.


(A) their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as

(B) its suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment as well as

(C) their suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment but also

(D) its suppliers’ operations, dictating not only the number of stitches and the width of the hem in every garment but also

(E) their suppliers’ operations, dictating the number of stitches, the width of the hem in every garment, and

1) "the chain" proper pronoun is "its"
2) We are left with B and D. Correct idiom is "not only x, but also y"
So the correct answer is D!
Simple

D is the correct answer.
Idion usage: not only X but also Y
SV Agreement chain... it's

Answer: D

Error1:
Pronoun Agreement: Singular Noun "The Chain" requires Singular Pronoun "It" instead of "Their"
Elimiate A,C,E

Error2:
Idiom: Not only... But also...
Eliminate B

Official Explanation:

In A, C, and E, the pronoun (their) does not agree in num­ber with the noun (chain) to which it refers. Choices A and B do not properly complete the construction beginning with not only: the correct version of the sentence should contain the phrase not only ... but also. The best choice for this ques­tion is D.
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daagh
I considered the chain of retail stores as plural Can you please explain how it is singular ?

teaserbae

mark the word 'the chain'. A chain may contain several rings or keys. Still, it is only one chain. 'The' also denotes individuality.
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Can anyone please explain what the word 'dictating' modifies?

Since it is an -ing verb, it should modify action in the preceeding clause. In that case, does it modify 'became involved'? If so, how does it make sense?

Please explain.

Posted from my mobile device

Becoming involved was in the form of dictating
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Thank you. Your explanation makes sense!

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