A:thought; had lost
B:think; lost
C:think; had lost
D:thought; have lost
如图,四面体ABCD中,O、E分别是BD、BC的中点,CA=CB=CD=BD=2,AB=AD= 2 .
(Ⅰ)求证:AO⊥平面BCD;
(Ⅱ)求异面直线AB与CD所成角的余弦;
(Ⅲ)求点E到平面ACD的距离.
连词成句。