A:interviewing; to prepare
B:interviewed; to prepare
C:interviewing; preparing
D:being interviewed; preparing
______take your kite with you tomorrow? ( )
已知正四棱柱ABCD-A1B1C1D1中AA1=2AB,E为AA1的中点,则异面直线BE与CD1所成的角的余弦值为 ( )
动脉血和静脉血的区分标准是