You dont have the option to format text as "hidden" in PowerPoint. You could
apply the same color as the background. Or you could cover it with a
background-colored rectangle. Or you could make the answer appear with an
animation after the question has been answered.

Kind regards,
Ute

If you are interested in learning VBA, I have a sample download that
provides for 10 Review Questions.  Actually all you need to do is to type in
your multiple choice questions and choices.  You only need to learn a little
about the code if you want to assign the correct answer to a different
choice.  The link to it is (bottom sample):

http://www.pttinc.com/cbt_development.html

I'm not clear what you are trying to do.  If you want a regular quiz,
Bill's example or some of my own in Chapter 7 Examples:

http://www.loyola.edu/education/PowerfulPowerPoint/

might be what you want, but you seem to be presenting a quiz.  You say
you don't want the answer to show up on the slide.  Why do you need to
put the answer on the slide at all if it is not going to show up?  Or, do
you want to show a question, discuss it is as a class and then have the
right answer show up?  This could be done with a simple animation.  Just
set the entrance animation effect to something for the answer.

If none of the suggestions here (by Ute, Bill, or me) work for you, maybe
you could describe in more detail what you want to do.

--David