A:having been picked out; was set
B:to have been chosen; set
C:to be picked out; was set
D:to have been chosen; was set
如图,在正方体ABCD﹣A1B1C1D1中,
(1)求证:AD1⊥平面CDA1B1;
(2)求直线AD1与直线BD所成的角.
“一花独放不是春,百花齐放春满园”在国际文化交往中,我们应( )
①吸收外来文化,不持立场
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如图,小方格的面积是1,则图中以格点为端点且长度为5的线段有( )