A:a
B:while
C:the moment
D:the more
3,-1.5, −312 ,0,2.5,-4.
(Ⅰ)当点M为EC中点时,求证:BM∥平面ADEF;
(Ⅱ)当平面BDM与平面ABF所成锐二面角的余弦值为 66 时,求棱锥M﹣BDE的体积.