Answer:
See below
Step-by-step explanation:
Macbeth! One of Shakespeare's better plays (Romeo and Juliet can rot for all I care)
Birnum is a forest and Dunsinane is a location so basically the witches are saying Macbeth will only be defeated if wood from birnum moves to Dunsinane. Which Macbeth interprets (wrongly as we find out later) as he will only be defeated if trees start walking, which is basically never