A:使用的用电器总功率过大
B:插座中的两根导线的线头相碰了
C:拉线开关中两根导线的线头相碰了
D:保险丝的规格不符合规定的要求
(Ⅰ)求证:平面PAD⊥平面ABCD;
(Ⅱ)设Q是棱PC上的点,当PA∥平面BDQ时,求二面角A﹣BD﹣Q的余弦值.
_____ the students came from different countries, they got along quite well in the summer camp.