平移刚体上任一点的轨迹有可能是空间曲线，而平面运动刚体上任一点的轨迹则一定是平面曲线。
查看答案
若某一瞬时平面图形上各点的速度矢量相等则平面图形的运动一定是平移。
A. 对
B. 错
2011.123.I'm sorry to tell you that the materials you wanted are ________.
A. taken off
B. put up
C. sold out
D. got off
2010.127.Even in small companies, computers are a(n) ______ tool.
A. natural
B. essential
C. careful
D. impossible
2011.125.________I am concerned, it is important to get a job first.
As long as
B. As well as
C. As soon as
D. As far as
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