必然事件的概率是______，不可能事件的概率为______．

--- _____do you study for a test?

---By reading the textbook.

A．What

B．When

C．How

D．Where

根据句意和汉语提示，填写单词。

1. Don't forget to _________ (锁) your bike. Five bikes were lost last night.

2. The children _________ (冲,奔) out of the school when the bell rang.

3. Yesterday the girl _________ (违反) the rule and her teacher was angry.

4. When I was about to read my book, I found I had ________ (忘了带) it at home.

5. He _________ (睡过头) this morning and went to school late.

液压传动是依靠（）来传递运动。

A、压力的变化

B、流量的变化

C、密封容积的变化

D、速度的变化

、门的把手一般都安装在离门轴远的一端，如图10所示。其中的科学道理是（）

A．根据杠杆的知识，推开门时比较省距离

B．根据杠杆的知识，推开门时比较省力

C．根据功的知识，推开门时手对门做功较慢

D．根据功的知识，推开门时手对门做功较少

近距离照射时，剂量计算误差的原因是（）。

A.放射源剂量强度高

B.放射源剂量分布的各向异性

C.放射源剂量分布的高梯度变化

D.放射源体积小

E.放射源包壳不均匀