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问题 问答题

如图（甲）所示，将敲响的音叉接触水面会溅起水花．这表明：声音是由于物体______产生的．图（乙）中敲响的右侧的音叉，与左侧音叉接触的塑料小球会弹起，这是因为______．

答案

将敲响的音叉接触水面会溅起水花．这表明：声音是由于物体振动产生的；

敲响的右侧的音叉，与左侧音叉接触的塑料小球会弹起，这是因为空气可以传声．

故答案为：振动；空气可以传声．

单项选择题

In bringing up children, every parent watches eagerly the child’s acquisition (学会) of each new skill--the first spoken words, the first independent steps, or the beginning of reading and writing. It is often tempting to hurry the child beyond his natural learning rate, but this can set up dangerous feelings of failure and states of worry in the child. This might happen at any stage. A baby might be forced to use a toilet too early, a young child might be encouraged to learn to read before he knows the meaning of the words he reads. On the other hand, though, if a child is left alone too much, or without any learning opportunities, he loses his natural enthusiasm for life and his desire to find out new things for himself.
Parents vary greatly in their degree of strictness towards their children. Some may be especially strict in money matters. Others are severe over times of coming home at night or punctuality for meals. In general, the controls imposed represent the needs of the parents and the values of the community as much as the child’s own happiness.
As regards the development of moral standards in the growing child, consistency is very important in parental teaching. To forbid a thing one day and excuse it the next is no foundation for morality (道德). Also, parents should realize that "example is better than precept". If they are not sincere and do not practise what they preach (说教), their children may grow confused, and emotionally insecure when they grow old enough to think for themselves, and realize they have been to some extent fooled.
A sudden awareness of a marked difference between their parents’ principles and their morals can be a dangerous disappointment.

Eagerly watching the child’s acquisition of new skills ______.

A．should be avoided

B．is universal among parents

C．sets up dangerous states of worry in the child

D．will make him lose interest in learning new things
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问答题

自行车是我们熟悉的交通工具。从自行车的结构和使用来看，它涉及不少有关摩擦的知识，例如：

A．轮胎上刻有花纹；

B．车轮做成圆形；

C．塑料套紧套在车把手上；

D．脚踏板凹凸不平

E．刹车时用力捏闸；

F．车轴处装有滚珠；

G．车的把手上有凹槽；

（1）上述各项内容中属于（只填写各选项前的字母）

通过改变接触面粗糙程度而增大摩擦的是：________；通过增大压力而增大摩擦的是：____________；通过变滑动为滚动而减小摩擦的是：________；

（2）请你大胆发挥想象：“假如没有摩擦”，自行车会出现什么样的情况?_______________（写出一个合理的场景）。

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