剪力撑吹瓶夹角应满足（）至（）
A.15°，30°
B.30°，45°
C.45°，60°
参考答案：C
It is certain that he will _____ his business to his son when he gets old. [ ]
A. take over
B. think over
C. hand over
D. go over
如图所示，物体以120J的初动能从斜面底端向上运动，当它通过斜面某一点M时，其动能减少80J，机械能减少32J，如果物体能从斜面上返回底端，则物体到达底端的动能为（ ）
A．88J
B．24J
C．20J
D．4J
