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问题 解答题

用科学记数表示：（1）691000=______，（2）0.00000047=______，（3）-321400=______．

答案

691000=6.91×105．

0.00000047=4.7×10-7．

-321400=-3.214×105．

故答案为：6.91×105，4.7×10-7，-3.214×105．

完形填空

Attention! Our earth has been facing a serious threat—global warming.

According to some _____ (专家), thousands of people die of hot wave小题1:. ____________

a    (每年), and the ice in the poles has been becoming thinner and thinner小题2: ____ year by year, _____ leads to the rise of the sea level and is threatening小题3:_____ many areas of the world, especially those coastal areas. On the 小题4:____________ hand, ______ (自然) disasters, like flooding, are more or less connected with小题5: ____________the global warming, and it’s o     that all these are the punishments 小题6:_______from nature. To look back, in the past five _____, that’s half a century, 小题7:____________we’ve destroyed our environment _____ random to develop the economy小题8:____________by _____ (滥用) oil and by using private cars instead of public transport.小题9:___________These r     in the rise of greenhouse gases in the atmosphere, causing小题10:____________the global warming.
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单项选择题

工艺系统的热变形只有在系统热平衡后才能稳定，可采取适当的工艺措施予以消减，其中系统热平衡的含义是（）。

A.机床热平衡后

B.机床与刀具热平衡后

C.工件和夹具热平衡后

D.机床、刀具与工件热平衡后
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