题干
The students wanted to know ___________.
A：whether light goes faster than sound
B：how many colors were there in a rainbow
C：that the moon travels around the earth
D：what would the world be like in the future
答案(点此获取答案解析）
A
C之间做简谐运动，规定以向右为正方向，图2是它的速度v随时间t变化的图象．下面的说法中正确的是 
图1 图2
