Time needed: 1min, 26s

Process of elimination:
1)The correct idiom is "Not only X but also Y". Eliminate A.
2)In B there is a change in meaning, since the "she believed..." part is not included.
3)In C "themselves" is useless. Eliminate C.
4)E uses the future tense, which is incorrect if you analyze the meaning of the sentence, and is unnecessarily wordy. Eliminate E.

D is concise, uses the correct parallelism and conveys the right meaning.

Correct answer: D

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MANHATTAN REVIEW OFFICIAL EXPLANATION:

The correct expression is ‘not only...but also...’. Eliminate A. B changes the meaning by eliminating ‘she believed’. Choice C is inefficient as it uses the word ‘themselves’. Choice E uses the wrong tense, the present. Choice D is the correct answer.
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I wonder why the idiom "not only .... but" is incorrect?

I saw another example in which the idiom "not only .... but" is correct.



By pressing a tiny amount of nitrogen between two diamonds to a pressure of 25 million pounds per square inch, scientists not only were able to transform the gas into a solid, but they also created a semiconductor similar to silicon.

(A) not only were able to transform the gas into a solid, but they also created
(B) not only were able to transform the gas into a solid but also creating
(C) were able not only to transform the gas into a solid but to create
(D) were able not only to transform the gas into a solid but also creating
(E) were not only able to transform the gas into a solid, but they were also able to create

The correct answer is C.


Expert please explain.

Thank you

Please help why the Idiom, not only-but is incorrect. It is used in GMAT.