Supposing you're talking about the scene 4 of Act I, the most accurate answer, in my opinion, is B. his controlling nature.
Throughout the play, Macbeth also displays his lack of confidence. But here, in this scene, his controlling nature prevails. As soon as he hears that Malcolm will be the Prince of Cumberland, therefore his greatest opponent, he has an idea to murder him. Now he believes the weird sisters' prophecy will come true, but not without his action. And he is resolved to commit to that cause, bloody and dishonest though it may be.
