-- big success the charity show was!
-- We collected a lot of school things.
A:How
B:What
C:How a
D:What a
人体发育过程中,性发育和性成熟的时期是( )
长方体ABCD﹣A1B1C1D1中,AB=2,AA1=AD=4,点E为AB中点.
(1)求证:BD1∥平面A1DE;
(2)求证:A1D⊥平面ABD1.