Answer:
a. Macbeth kills the current king and is rewarded by being named king himself.
Step-by-step explanation:
Fair is foul and foul is fair, is a recurring theme in Macbeth, it´s first stated by three witches at the begining of the play, but it is used to say that not everything that seems god is good, and not everything that seems bad is bad, in this case when Mcbeth kills the current king and no one knows he did it, he is Kinged because they think of him as a noble Knight, not knowing that he murdered the late king and should be trialed for that.