KAPLAN OFFICIAL EXPLANATION:

This sentence compares the invention of the printing press to that of the computer, and since the initial, nonunderlined portion of the sentence uses the simple past tense (led), the remainder of the sentence, continuing as it does to discuss a past event, must also use the simple past tense. Therefore, eliminate (A), (B), and (C) for including incorrect verb tenses. (D) and (E) give you different options for the final verb. Since the invention of the computer is the subject of this part of the sentence and is singular, the verb must be singular as well. Eliminate (D), and (E) remains.

An 800 test taker is aware that the subject of a sentence can come after the verb, particularly in constructions beginning with there are or there is.
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A seems to be idiomatically correct. C and E dont seems to be idiomatically correct. Use of past tense in D is incorrect.

Sent from my Redmi Note 3 using GMAT Club Forum mobile app

+1 for E.

(A) what has been equally significant in the twentieth century is

(B) equally significant in the twentieth century has been

(C) no less significant in the twentieth century is

(D) what was equally significant in the twentieth century were

(E) no less significant in the twentieth century was --> Correct, rectifies Verb-Tense error

Hence, E.
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dvishal387
Firstly, option A is utterly incorrect because it uses "has been" - invention was one time event, and not an ongoing event
Secondly, I don't see any idioms as such in options for the option to be incorrect, and there is hardly any idioms in any of the option.
Thirdly, the option must have a past tense, because the invention happened in twentieth century, so the use of present tense is wrong.

Hope it helps!
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IMO E.

Invention was a one time event and past tense is required to indicate the timing of the invention of computers. Only D and E do that. D has SV mismatch. Hence, E.

Correct Answer must be (E) for the highlighted errors in other options...
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(A) HAS BEEN IS WRONG
(B) SAME AS A
(C) IS WRONG FOR PAST EXPRESSION
(D) WERE DOESN'T AGREE WITH SINGULAR SUBJECT
(E) IS THE CORRECT ANSWER.
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