前照灯的组成和功能。
参考答案：前照灯主要由反射镜、配光镜和灯泡组成。
反射镜的功能：尽可能收集灯泡发出的光线，并将光线聚合成很强的光束射向远方。50W的灯泡，无反射时只能照亮6M，而经反射后可照亮150M。
配光镜的功能：弥补反射镜光束太窄而照明范围过小的缺陷，保证行车时路面的有均匀的照明。
灯泡：产生光源，常用的灯泡有普通灯泡、卤钨灯泡和高压氙灯三种。
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| Tom __1__ a very good student, and he __2__ doing homework, because he liked __3__ other things in his free time. Usually he didn’t do __4__ homework, and when he did it, he always made __5__ mistakes. Then one day, his maths teacher looked __6__ Tom’s homework and found that he had done __7__ right. He was very happy and very surprised. He asked Tom to his desk and __8__ to him, "You have done all your homework right this time, Tom. __9__ your father help you?" Usually Tom’s father did help him with his homework, but this time he didn’t, because he was not at home. Tom answered, "No, sir. He was busy last night, so I had to do it all _10__ myself." | |||
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