Why does macbeth give the order to have banquo and his son killed?

Hope I help

He worries that Banquo will be suspicious of Duncan's murder, since he was there when Macbeth received the prophecy that he would be king. He also wants to avoid a “fruitless crown,” so he decides to kill Banquo and his son Fleance in order to ensure that none of Banquo's “issue” take the throne after him.

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the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).

c? not a 100% sure

explanation: