Macbeth murders Duncan and becomes the king of Scotland. However, he is insecure in his position as he remembers the witches' prophecy that Banquo’s descendants will be kings. His ambition makes him plot other killings, but his plans start going awry. Which event is the turning point in Macbeth?

A)the murder of Duncan
B)the murder of Banquo
C)the murder of the guards
D)the murder of Macduff’s family