The small shop ________ for several years.
A:opened
B:has been opened
C:has opened
D:has been open
函数y=﹣x+1与函数y=-2x在同一坐标系中的大致图象是( )
如图,四棱锥P﹣ABCD的底面是正方形,PA⊥底面ABCD,PA=2,∠PDA=45°,点E、F分别为棱AB、PD的中点.
(Ⅰ)求证:AF∥平面PCE;
(Ⅱ)求证:平面PCE⊥平面PCD;
(Ⅲ)求三棱锥C﹣BEP的体积.