Which of the following represents an external conflict?

a. Before Macbeth kills King Duncan, he imagines he sees a dagger floating in the air in front of him.

b. Macbeth regrets killing King Duncan, although he would do it again if necessary.

c. Macbeth wants Banquo dead, so he hires men to murder him.

d. At the banquet, Macbeth's guilty conscience conjures up an image of the dead Banquo.