单项选择题
下面关于振弦式（弦振动法）应变仪的描述，正确的有 A 弦振动法测...
多项选择题下面关于振弦式（弦振动法）应变仪的描述，正确的有 A 弦振动法测试的基本参数为基频 B 测试值越高，表明弦的张力越大位移也越大 C 与电阻式应变仪一样，也需要温度补偿 D 上述说法均不对
下面半剖视图表达正确的一组是（ ）A.B.C.D.
单项选择题下面半剖视图表达正确的一组是（ ） A. B. C. D.
Light travels at a speed which is about a million times...
单项选择题Light travels at a speed which is about a million times faster than the speed of sound. In one second, light travels about 300,000 km. But sound travels only 344m. You can get some idea of his 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 born.Thus, if you want to be honest, you can 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. "We can know from the information given in the passage that the moon must be about ____ away from us.（ ）
B.
C.
D.
