"He is not available at the moment."
Translation:Hij is momenteel niet beschikbaar.
I always wonder with these questions, whether part of some of the other sentences is correct. For example, was the "op het ogenblik" another way of saying "at the moment"?
'Op het ogenblik' is indeed 'at the moment'. Equally used is 'op dit ogenblik', which is, of course, 'at this moment'.
Note that we can't see the other possible answers for the mpc questions, so I can't help you much further than this. :)