Here is one way: you could do that with a very tiny macro if you set up the document with multilevel list styles.

level 1 style = Question
level 2 style = A, B
level 3 style = Answer:

All your macro need do is toggle the hidden text property of the level 3 style. There would be one modification if you wish to make it that easy. That is, for your level 1 paragraphs, include the text of the question inline with the same paragraph to avoid the need for a style separator or hidden paragraph mark. Hope this helps.