A:hand i
B:hand out
C:hand dow
D:hand over
1956年中共“八大”的召开,是探索建设社会主义道路的良好开端( )
— I'll be away on a business trip. Would you mind looking after my cat?
— Not at all. ________________.
(Ⅰ)证明: BM⊥平面AEC ;
(Ⅱ)求 MC 与平面 DEC 所成的角的余弦值.