In the Context of Black Holes, the Word "Ergosphere" Names

In the context of black holes, the word "ergosphere" names the

A) entire region inside the event horizon.
B) region just outside the event horizon of a rotating black hole where it is impossible for anything to remain at rest.
C) entire universe outside the black hole.
D) region occupied by the accretion disk where matter from a companion star collects around a black hole.