Which must be true? point a is the center of the circle that passes through points e, f, and g but is not the center of the circle that passes through points x, y, and z. Point a is the center of the circle that passes through points x, y, and z but is not the center of the circle that passes through points e, f, and g. Point a is the center of the circle that passes through points e, f, and g and the center of the circle that passes through points x, y, and z. Point a is not necessarily the center of the circle that passes through points e, f, and g or the center of the circle that passes through points x, y, and z.