The First Apparition tells an eager Macbeth that he should fear Macduff, saying "beware Macduff; / Beware the Thane of Fife...." The Second Apparition reassures Macbeth that "none of women born / Shall harm Macbeth" and the Third Apparition tells Macbeth he has nothing to fear until "Great Birnam wood" moves to "high ...
I'm not 1000% confident in this answer but I believe it's B) to inform readers about the tactics Sparta and Rome used to hold cities and their effectiveness
