Answer: D. that people cannot exert control over supernatural elements
Explanation:
When the three apparitions were summoned for Macbeth, they spoke to him but didn't answer his questions. The apparitions summoned were the armed head, a child crowned, that had a tree in his hand and a bloody child.
The apparitions told Macbeth to be careful of Macduff but despite that he was assured that no one can harm him and that he won't be overthrown until when Birnam Wood eventually moves to Dunsinane.
The three apparitions not answering his questions indicates that people cannot exert control over supernatural elements.