（4分）为了探究光反射时的规律，小明进行了如图所示的实验：
（1）图中的光屏是一个可折转的硬纸板，此光屏在实验中的作用是：① ________________ ；
②用来验证 。
（2）在探究反射角与入射角的关系时，小明同学分别测出了反射角、入射角分别是400，于是他就得出了反射角等于入射角的结论。请问他这样做是否正确？ ________________ ，理由是________________ 。
（1）显示光路 三线共面 （2）不正确 具有偶然性，应该多测几组数据。
题目分析：(1)沿着纸板入射光线，可以能够具体显示出光路。纸板是一个平面，可以观察三线是否共面。（2）只测量一次实验数据就得出结论具有偶然性，不能有效减小误差，应该多测几组数据。
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| We are lucky to live in a rich country where we have many things. However, most of us usually 1 some things. Electricity is one thing 2 we waste most. Lights, TVs, 3 and other things are often kept on even when no one is using them. We should turn them off when we do not need them. It 4 less than a second to do it. Anyhow, not wasting electricity save money, because we do not have to 5 the electricity we do not use. The second thing that we often waste is water. Fresh water is precious*, 6 it shouldn't be wasted. It is only a simple matter of turning off a tap*. I am sure 7 can do this easily if he wants to. 8 big waste is food. My mother 9 cook so much food that much of it was thrown away. I told her we had wasted so much 10 . She thought I was right and now cooks 11 what we can eat. It is not 12 to be wasteful. I find there is a simple 13 of not wasting things. That is to use only what we 14 . Do not touch what we do not need. 15 this way we can stop being wasteful. | ||||
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