Are congruent circles always concentric circles?

A) yes, if they are congruent then they must have the same size and center
B) no, it is not possible for two circles to be the same size with the same center.
C) sometimes, if they have the same center and the same radius length they will be both congruent and concentric.
D) sometimes, if they have the same center and the same chord length then they will be both congruent and concentric.