What are the characteristics of Archaebacteria?

What are the characteristics of Archaebacteria?

A) They are single cells that have a nucleus and tend to live in moderate conditions.
B) They are single cells that lack a nucleus and tend to live in extreme conditions.
C) They are single cells that lack a nucleus and tend to live in moderate conditions.
D) They are single cells that have a nucleus and tend to live in extreme conditions.