Final answer:
Macbeth's line "We have scorched the snake, not killed it" refers to the incomplete resolution of threats to his power, particularly relating to Banquo's murder plot which he believes has not fully secured his position.
Step-by-step explanation:
When Macbeth refers to the snake that "We have scorched the snake, not killed it" in Act III, Scene II, he is metaphorically speaking of the incomplete nature of his actions. Macbeth is alluding to the fact that they have only dealt with part of the problem and fears the consequences of their deeds, as the real threats to his power — notably the other characters who may suspect or challenge him — are not entirely eliminated. Specifically, this line refers to Banquo's murder plot (C), as Macbeth has arranged to have Banquo killed to prevent the witches' prophecy that Banquo's descendants will become kings from coming true.