Answer: B. His sons, Malcolm and Donalbain
Both Macbeth and Lady Macbeth are intent on killing Duncan, although Macbeth hesitates more. However, the desire to be king is stronger, and Macbeth stabs Duncan while he is asleep. The next morning, Macbeth pins the murder on the chamberlains and kills them. He assumes the kingship. Duncan's sons, Malcolm and Donalbain, flee to England and Ireland, as they are scared they will be killed as well. This makes it easy to consider them as the primary suspects of the murder.
