Part A: The most fitting answer to the question about the irony of Achilles's reaction to Odysseus’s gift of the swords is:
A. Thetis’s plan to keep Achilles safe is undone by Achilles himself.
Part B: The excerpt that BEST supports the answer in Part A is:
C. "Achilles could not conceal his excitement when he saw the weapons. He seized them and revealed his identity, after which he joined the Greeks in their fight against the Trojans." (Paragraph 4)
This excerpt highlights how Achilles's desire to embrace his heroic identity leads him to reveal himself, which ultimately undermines Thetis's plan to keep him hidden for his safety.