Final answer:
King Duncan orders the execution of the disloyal Thane of Cawdor and awards the title to Macbeth for his valor. So, the best answer is a, The Thane of Glawis should be executed.
Step-by-step explanation:
King Duncan in Shakespeare's Macbeth believes that the Thane of Cawdor should be executed for disloyalty, and hence, he decides to bestow the title of Thane of Cawdor on Macbeth as a reward for his loyalty and bravery in battle.
This decision is communicated in Act 1, Scene 2 where Duncan declares, "No more that thane of Cawdor shall deceive Our bosom interest: go pronounce his present death, and with his former title greet Macbeth."
Therefore, the correct answer to the question is that Duncan believes A) The Thane of Glawis should be executed (although it should be noted that the correct title is Thane of Cawdor).
So, the best answer is a, The Thane of Glawis should be executed.