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  3. Light travels at a speed which is about a million times faster than the speed of sound. In one second, light travels about 300,0

Light travels at a speed which is about a million times faster than the speed of sound. In one second, light travels about 300,0

admin2012-11-20  66
问题     Light travels at a speed which is about a million times faster than the speed of sound. In one second, light travels about 300,000km. But sound travels only 344m. You can get some idea of this difference by watching the start of a race. If you stand some distance away from the starter, you can see smoke comes from his gun before the sound reaches your ears.
    This great speed of light gives us some strange facts. Sunlight takes about 8 minutes to reach us. If you look at the light of the moon tonight, remember that the light left the moon 1.3 seconds before it reached you. The nearest star is so far away that the light which you can see from it tonight started to travel towards you four years ago at a speed of nearly 2 million km per minute. In some case, the light from one of tonight’s stars started on its journey to you before you were bola.
    Thus, if you want to be honest, you cant say" The stars are shining to night"? You have to say "The stars look pretty. They were shining four years ago but their light has just reached Earth".
If the information give in this passage is correct, when we look at a star at night ______.
选项 A、we will notice that it is not moving
B、we cannot tell whether or not it still exists
C、it will be brighter than the moon
D、it is four years that the light we can see will reach us
答案B
解析
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