A:60°
B:90°
C:120°
D:180°
如图反映四个国家的人口出生率和死亡率.据此回答下题.
如图,在四棱锥A﹣BCDE中,平面ABC⊥平面BCDE,∠CDE=∠BED=90°,AB=CD=2,DE=BE=1,AC=2.
(Ⅰ)证明:AC⊥平面BCDE;
(Ⅱ)求直线AE与平面ABC所成的角的正切值.
从方框中选择适当的短语,并用其正确形式填空。
as long as because of according to how about was full of