What evidence suggests that the dagger macbeth sees is an illusion

In this passage from Act II, Scene I, "The Tragedy of Macbeth", by William Shakespeare, the statement that suggests that the dagger is an illusion is option D. A false creation, / Proceeding from the heat-oppressed brain? Macbeth, before killing King Duncan, sees a dagger in the air with its handle towards him and its tip towards Duncan. He doesn't know whether it is real or not.