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问题 填空题

草地上静止的足球被足球运动员踢出去，足球由静止运动起来，这是因为______．踢出去的足球能够继续向前滚动，这是因为______．足球在草地上越滚越慢，这是因为______．

答案

足球由静止运动起来，这是因为足球受到脚的作用力；

踢出去的足球由于惯性，能够继续向前滚动；

足球在草地上滚动时，受到草地阻力的作用，所以越滚越慢．

故答案为：足球受到脚踢的力；惯性；足球受到草地的阻力．

填空题

根据句意和中文意思或所给词，写出正确的单词。

1. You are ______ (suppose) to shake hands when you meet a Chinese friend.

2. Keep your eyes ______(close) when you are doing eye exercises.

3. A knife is used for _______(cut) things.

4. Trees can keep water from _______ (run) away.

5. Everything was ______( familiar ) with me because I was in Japan for the first time?

6. Do you still remember______(看见) me somewhere in Beijing ?

7. Give up bad _________ (举止) and be polite.

8. ________ ( 花 ) time with family and friends is very important.

9. He is _________ (满意)with his son.

10. People are pretty _______( 宽松 ) about time in Colombia.
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选择题

氢原子的能级如图所示，一群氢原子处于n=3的能级，向较低能级跃迁过程中，辐射的光子

A．频率最多有3种

B．频率最多有2种

C．能量最大为12.09eV

D．能量最小为10.2eV
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