极板间距为d的平行板电容器,充电后与电源断开,此时两极板间的电势差为U 1 ,板间电场强度大小为E 1 ;现将电容器极板间距变为 ,其它条件不变,这时两极板间电势差为U 2 ,板间电场强度大小为E 2 ,下列说法正确的是 A.U 2 = U 1 ,E 2 = E 1 B.U 2 = 2U 1 ,E 2 = 2E 1 C.U 2 = 2U 1 ,E 2 = E 1 D.U 2 = U 1 ,E 2 = E 1