Sentence Correction

The scientist knew for a long time beyond the shadow of a doubt that she discovered the double helix.

A) The scientist knew for a long time beyond the shadow of a doubt

B) For a long time, the scientist had known beyond the shadow of a doubt

C) For a long time, the scientist had known with great certainty

D) For a long time, the scientist knew beyond the shadow of a doubt

E) The scientist had known for a long time beyond the shadow of a doubt

[spoiler]IMO : B
OA: C[/spoiler]

What is the source of this question? Not likely a decision that you will have to make on the GMAT...

I just google it..

Yeah, stick with the official stuff - much more to learn with those questions...