Answer:
2. They prevent others from suspecting that he is the murderer.
Explanation:
In this section, we learn that Macbeth is obsessed with having power due to the witches' prophecies. In order to ensure that this will come to happen, he kills Duncan. However, he does not want anyone to find out, so he pretends that he was unaware of the murder, and kills the guards. All of these is meant to prevent others from suspecting that he is the murderer.