sound travels at 340 meters per second in air.travels 为什么用at?

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• 八下 英语 选词填空before,discover,fast,in,come,watch,so,fast,it,ago,shine,not canLight travels at a speed which is about a million times ( ) than that of sound.( ) one second,lidht travels about 300,000 kilomemters,but sound traves only 340 meters.You can get some idea of this gifference by ( ) the start of a running match.If you stand far away from the starter(发令员),you can see smoke ( ) from his gun ( ) the sound reaches your ears.The fastspeed of light prod
• sound travels at 340 meters per second in air.travels 为什么用at?
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