Answer: A.The allusion highlights the idea of avenging a father’s murder.
In the myth of the Trojan War, we learn of Pyrrhus, son of Achilles. Pyrrhus ends up killing Priam, the King of Troy himself, who was responsible for the war, and therefore, the death of his father Achilles. Pyrrhus is delighted to avenge the death of his father and does so in front of Hecuba, Priam's wife.
Hamlet uses this story to show that his intention is to similarly avenge his father's death by killing Claudius, who is also a king. In this comparison, Claudius is Priam, Hamlet is Pyrrhus and Gertrude is Hecuba.