I will go with B

Praveen what is source of this quistion?

[spoiler]Source: 800score.com[/spoiler]

between C and D
finally D

I was torn between C and D and, like the previous individual, I'll opt for D. What's the OA?

OA D

Please provide explanations

kvcpk wrote:Though the Pythagorean theorem is attributed to Pythagoras, a mathematician and philosopher who lived in the 6th century BC, the first proof had not been completed before the year 300 BC, when it appeared in Euclid's Elements.

A. the first proof had not been completed before the year
B. it had not been proven to be true before the year
C. the first proof of the theorem was not completed prior to
D. the first proof was not completed until
E. it was not proven to be true prior to

Some thoughts:

--> Past perfect tense is used when we have two related works performed in the past. One of them is done before other one.
=> See the examples:

I had not done the work before 1990.

==> here, A single work that was not done before 1990. So, the use of past perfect in this case is incorrect.

==> This kills the options A and B.

Prior to/Before/Until:

"Prior to" is NOT liked by GMAT. I have found some questions in GMATPREP. Prior to' has been used in the wrong options.

The work was not done before 1990.
--> This may mean that the work may be done after 1990.
--> In this case "before" can be replaced by "until". It makes the sentence more flowing.

The work was not done until 1990.
--> This means that was done within 1990.

This kills the options C and E.

More:

The work was not done before the year 1990.

==> Mind it. 1990 itself is a year, so the use of "the year 1990" is simply redundant.

In the option C, the repeat of the word "theorem" is redundant because it has already been mentioned.

Example:
Though the movie Avatar was not released until 2010, the first premier show of the movie was shown in Hollywood.

The red part is not just necessary.

So, answer is D.

GMAT prefect ...thanks.

Nicely explained