（Ⅰ）证明：ED∥面PAB；
（Ⅱ）若PC=2，PA= 3 ，求二面角A﹣PC﹣D的余弦值．
Has John Beijing Shanghai?
—What do you think of the boy's painting?
—I've never seen a person with sense of art.
下列关于光现象的说法正确的是（ ）
