Hydra is biologically believed to be immortal.

Answer: Option B

Immortal : living forever; never dying or decaying.
Undying : (especially of an emotion) lasting forever.
Perishable : (especially of food) likely to decay or go bad quickly.
Ancient : belonging to the very distant past and no longer in existence.
Eternal : lasting or existing forever; without end.

Antonym of Immortal is Perishable