My name is Chen Lan. My home is in Gulangyu. Do you know it? It is in Xiamen. It is near the sea(海). Gulangyu is a small place，but it is very nice and clean. There are no cars，no buses. People only walk. So it is very quiet.
   Our house is in the middle of Gulangyu. Behind our house there is a big old tree. My grandfather tells me that the tree is very，very old. There are many birds in the tree. We call it a “bird tree”. Our house is near the sea. The sea is big and blue. There are a lot of fish in the sea. After school，I go there and catch(捉) fish with my friends. It is very interesting. I like fish and I like catching fish.

（Ⅰ）证明：BC₁∥平面A₁CD；

（Ⅱ）设AA₁=AC=CB=2，AB=2 $\sqrt{2}$ ，求异面直线BC₁与A₁D所成角的大小．

人在争论时经常面红耳赤，与之有关的是（　　）

如图，在四边形ABCD中，AC平分∠BAD，且AC=BC，AB=2AD．

（1）求∠ADC的度数；

（2）若AB=10cm，CD=12cm，求四边形ABCD的面积．

“低碳经济”已成为经济发展的重要模式，实现“低碳经济”的一种策略是节能。下列制备氢气的方法最节能的是（   ）