(2023·娄底)如图,抛物线 =a(x)^2+bx+c 与x轴相交于点-|||-A(1,0)、点B(3,0),与y轴相交于点C,点D在抛物线上,当-|||-ykparallel x 轴时, CD= __(2023·娄底)如图,抛物线 =a(x)^2+bx+c 与x轴相交于点-|||-A(1,0)、点B(3,0),与y轴相交于点C,点D在抛物线上,当-|||-ykparallel x 轴时, CD= __