质量为M的物体从高处由静止下落，若不计空气阻力，在第1S内和第2S内重力做的功之比[ ]
A.2：3
B.1：1
C.1：3
D.3：5
答案：C
It was the photo of mine ______ was taken ________ stood the high tower.
A． which; that
B． that; that
C． that; where
D． who; that
当库存管理水平为中等水平时，库存面积有效利用的理想值为 ( )
A．70%
B．50%
C．60%
D．65%
