I would only see two answers that would be able to fit in this case. We can understand that 'irony' would be something as when there would be a case, but then there would be a twist that would turn it around and we can see in these options two cases.
a man challenges another man to a duel but only one man shows up to the duel
and...
A woman predicts that the child she is carrying is a boy only to find out that it is a girl.