The coming of “birnam wood to dunsinane” could be described as
a. a hallucination.
b. a symbol of guilt.
c. an army's use of camouflage.
d. a nightmare.
both c and d depending on the point of view; Malcolm's army uses it as camouflage and it is one of the things that the witches say will happen before Macbeth's death so it is his worst nightmare.