问题
单项选择题
当系统受到暂时干扰、系统的平衡状态遭到破坏时仅靠其弹性恢复力来维持的振动称为（）
A．自由振动
B．受迫振动
C．自激振动
D．干扰振动
答案
参考答案：A
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当系统受到暂时干扰、系统的平衡状态遭到破坏时仅靠其弹性恢复力来维持的振动称为（）
A．自由振动
B．受迫振动
C．自激振动
D．干扰振动
参考答案：A
Today is Sunday. Mike and Peter go to school. Listen! They are talking about the life in the room.  “ will the world be like? ”Peter asks. “I think that the world will be a place to live in. And we will machines and robots at home. They will help us do lots of , ”says Mike. “The robots will help cook dinner, clean the houses and old people. I think there will be a kind of medicine(药) it can make us live more than 100 years, ”Peter says. “What will you do then? ”says Mike. “Then I will my great-grandchildren(曾孙)to the moon, ”says Peter. “The moon? I will go to the Mars(火星)with my wife, ”says Mike.
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