船在静水中的航速为v₁，水流的速度为v₂．为使船行驶到河正对岸的码头，则v₁、v₂的方向应为（   ）

如图，在Rt△ABC中，∠ACB=90°，D为AB中点，AE∥CD，CE∥AB．

Problems relating to people’s livelihood have been the focus of the government, especially _______ ­­Premier Wen Jiabao included them in his government work report last year.

My dear child, I believe that you can solve the problems by y____.

将下列各数填入相应的集合中．

﹣7，0， $\frac{22}{7}$ ，﹣22 $\frac{1}{3}$ ，﹣2.55555…，3.01，+9，4.020020002…，+10%，﹣2π．

无理数集合：{   }；

负有理数集合：{   }；

正分数集合：{   }；

非负整数集合：{   }．