Refer to "The Godlike Achilles" from the What Happened Before the Iliad. In the story "The Godlike Achilles" from "What Happened Before the Iliad," why does Thetis dip Achilles into the river Styx?

She wants to prove her loyalty to the gods.

She is angry with Zeus for ruining her wedding.

She hopes it will make him immortal.

She wants him to rule the underworld.