Answer:
In Act 4, Scene 3 of "Macbeth," Ross lies to Macduff about the fate of his children because he does not want to tell Macduff the truth, which is that Macbeth has ordered their murder. Ross is aware that Macduff is one of Macbeth's enemies and that Macduff is likely to be devastated by the news of his children's deaths. Therefore, he decides to lie to Macduff in order to protect him from the pain and anguish that he would feel upon learning the truth. It is worth noting that this lie is ultimately revealed to Macduff later in the play, and it serves to further fuel his hatred and desire for revenge against Macbeth.
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