Hello. I need help making a choice loop in RPG Maker 2000. For example:

Question A requires Answer B as the correct choice.
However, Answers C & D are included too.
If I choose B, the game continues, but if I choose C or D
I have to start over.

Is this possible?

Yes, it is. You can do this with labels.
First, set up a label at the beginning of the choice selection (or the message box preceding it if you want that repeated as well). Then, in the sections for C and D, put at "go to label" that matches the number of the label you set up before after putting up the special C and D dialogue. It will kinda look like this:

<>Label 1
<>Message: Bla bla bla?
<>Show choices: A,B,C,D
<>
<>Thing for choice A:
<>Message: A thing
<>Thing for choice B:
<>Message: B thing
<>Thing for choice C:
<>Message: C thing
<>Go to label 1
<>Thing for choice D:
<>Message: D thing
<>Go to label 1
<>End choices
<>Message: you get here after choosing A or B

Hopefully I explained it well enough for you.