could have done- mean the same as it should have been done
all the other three makes no sense if you place it in the blank
should have failed- means that he failed..
other incorrect for the same reason that I've mentioned in the above answe
could have done- mean the same as it should have been done
all the other three makes no sense if you place it in the blank
should have failed- means that he failed..
other incorrect for the same reason that I've mentioned in the above answe