选一选。

二    一    十 

我有____只手。

我有____根手指。

每个人都有____张嘴。

 如图是一个弹簧门的示意图，相当于一个杠杆．弹簧的作用是当人进门后，它的能力自动将门关闭，在开门时它起到阻力的作用．

已知将门推到如图所示的位置时，推力F与门面垂直，它的力臂是0.8m，弹簧产生的阻力是120N，力臂是0.2m，求：

下列运算中，正确的是（    ）

根据材料内容，选择正确答案。

    Do you know fish come out of eggs when they are born? After the little fish comes out of the egg, it eats the food in the egg. When it is big, it leaves the egg. It swims in the water. You can see the eyes and nose. Its ears are hidden in the head.

    Spree fish eat other fish. Some fish have small mouths and teeth and they often eat plants.