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#c927ed0c-4a48-43b4-990f-da309c652549中等填空题动点问题立体几何

11.如图,正四棱柱ABCDA1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}中,AA1=2AB=2AA_{1}=2AB=2,点EEFF分别是线段AC1AC_{1}BDBD上的动点,则EFEF间最小距离为((  ))