如图,用斜面和滑块做“测物体平均速度”实验:(1)实验原理是 (2)如图,滑块自顶端出发时开始计时,滑至斜面底端时停止计时,此过程中滑行的距离s= cm,平均速度v= cm/s(3)实验时应使斜面坡度较小的目的是:方便测量 .为了减小时间测量的误差,可以采取的措施是 .The 12 million people in Mexico City woke up on
September 19th, 1985, to find their city ________ after the terrible quake.
A. in trouble B.
on purpose C.
out of work D. in ruins