（Ⅰ）证明：ED∥面PAB；

（Ⅱ）若PC=2，PA= $\sqrt{3}$ ，求二面角A﹣PC﹣D的余弦值．

有关亚马孙河叙述正确的是（  ）

读一读，选一选。

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(____ ) 2. Nice to meet you.        B. Nice to meet you, too

(____ ) 3. Colour it brown.          C. OK!

(____ ) 4. Good afternoon.         D.  Good afternoon