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Sentence Correction: Tenses - Past Simple and Progressive

Before the 8th century, philosophers were unsure whether "nothing" could be represented by a symbol or not.

While this answer choice fixes the original Redundancy error by eliminating the words or not after the term whether, it is grammatically incorrect. Before the 8th century is a specific point in time and indicates that this sentence should be in the Past Simple. However, this answer choice uses the Past Perfect (had been).

While this answer choice fixes the original Redundancy error by eliminating the words or not after the term whether, it is grammatically incorrect. Before the 8th century is a specific point in time and indicates that this sentence should be in the Past Simple. However, this answer choice uses the Present Perfect (have been).

In the GMAT, the addition of the phrase or not at any point after the word whether is considered redundant and, therefore, a stylistic error. Look for a more concise answer choice.

This answer choice repeats the original Stylistic error. In the GMAT, the addition of the phrase or not at any point after the word whether is considered redundant. Look for a more concise answer choice.

That is correct!

This answer choice corrects the original Redundancy error by eliminating the words or not after the term whether.

Before the 8th century, philosophers were unsure whether "nothing" could be represented by a symbol or not
Before the 8th century, philosophers had been unsure whether "nothing" could be represented by a symbol
Before the 8th century, philosophers have been unsure whether "nothing" could be represented by a symbol or not
Philosophers before the 8th century were unsure whether "nothing" could be represented by a symbol 
Philosophers before the 8th century were unsure whether or not "nothing" could be represented by a symbol