A:72
B:19
C:53
D:125
Miss Read is good ____________ music. She is good ____________ children in the music club.
—Yes, _____? I'll give them a call right now.
从侧面看到的形状是( ).
如图,四棱锥P﹣ABCD中,底面ABCD为菱形,且PA=PD=DA=2,∠BAD=60°
(I)求证:PB⊥AD;
(II)若PB=6,求二面角A﹣PD﹣C的余弦值.