The disappearance of crawling behavior in the tobacco hornworm (Manduca sexta) is the result of

A) a sharp reduction in ecdysteroid hormones in the adult stage.
B) degeneration of the proleg leg muscles just before the pupal stage.
C) replacement of existing neurons by new neurons that support a more sophisticated style of locomotion in the pupal stage.
D) the innervation of proleg retractor muscles in the larva.