1.  He  __________  gone,  even if he had wanted to, as he had to work late that evening.
must have
should not have
couldn't have

2.  We know perfectly well what we  __________  done.  But it´s a bit late to worry about that now.
would've
should've
must've

3.  Where do you suppose Pete is?  He  __________  forgotten about the meeting.
would've
should've
must've

4.  I  __________ been mistaken.  It can´t have been Peter I saw kissing that gorgeous girl.
would've
could've
must've

5.  He  __________  asked you to the party,  if he´d known you were in town.
should've
would've
must've

6.  They __________  fired John.  He was a good worker and I think they´ll regret it
mightn't have
must not have
shouldn´t have

7.  They  __________  work last Friday afternoon,  so they went for a picnic.
didn't have to
mustn't
didn't ought to

8.  If he had wanted to,  he  __________  been a doctor.  He was clever enough
could
could've
couldn't have

9.  She  __________  left it too late to apply to university this year.
would have
may have
ought not to have

10. You really should drive more carefully!  You  __________  killed someone!
might have
may have
would have