A:①②
B:②③
C:③④
D:①④
Put _______ your boots and your cowboy hat.( )
(Ⅰ)证明:PB∥平面AEC;
(Ⅱ)设二面角D﹣AE﹣C为60°,AP=1,AD= 3 ,求三棱锥E﹣ACD的体积.