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[audioFiles]audio_ezfm_0106(20104)[/audioFiles]

游客2024-10-24  37
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答案                                              Laser
     A laser is used to produce very powerful beams of light./Today laser is getting wider use in more fields./ Why is laser so much more powerful than other kinds of light? /
     Laser is a kind of light and also a form of energy./A laser beam is made up of very short waves . /These waves all have the same wavelength. /The laser beam keeps going on and off all the time./As these changes are very fast, we can but see them./During the time the laser beam is off,/the energy for the next burst of light is being built up,/so when the beam is on again, it will be a strong burst./And the laser beam doesn’t spread,/it doesn’t get wider and wider as other fight beams do./This is why the laser beam can keep all of its energy/and is so much more powerful than other light beams.
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