Question

a segment joining the center of a circle to a point of the circle. what would it be?
a chord of a circle that contains the center of the circle. what would it be?
circles that have equal radii. what would it be?
two or more circles that lie in the same plane and have the same center. what would it be?
the set of all points in a plane that are at a given distance from a given point in the plane. what would it be?