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阅读下面这篇短文，短文后有2项测试任务；(1)第23～26题要求．从所给的6个选项中为第2～5段每段选择1个正确的小标题；(2)第27～30题要求从所给的6个选项中选择4个正确选项，分别完成每个句子。

{{B}}Compact Disks{{/B}}
1 If someone says to you your music CDs don’t really hold any music on them, and they only have numbers recorded on them, you may not believe it. In fact, he is right in that sound is actually recored onto the CDs as special numbers --a digital code. The code is pressed onto the CD as bumps on a long spiral track almost five kilometers long. These bumps are an average of 0.5 microns wide.
2 A small laser beam shines onto the bumps as the CD turns. The light is reflected back to a receiver that records how the laser light bounces back. This lets the CD player turn the reflected light back into the original code. This means you can hear the original code as music.
3 Digital codes are used with many technologies. E-mail needs these kinds of code numbers. Spac

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