Answer:
C. Banquo and his son.
Step-by-step explanation:
Macbeth killed Banquo because he is the only one that suspects of Macbeth killing Duncan. One of the Witches´ prophecies was that Fleance, Banquo´s son would be King. So to prevent that and because Macbeth heard the prophecies aside with Banquo he decided to kill both of them.
I hope this answer helps you.