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问题 选择题

下列物质的名称、俗名与化学式完全对应的是                 [ ]

A.氢氧化钙     熟石灰   CaO          

B.碳酸钠         火碱       Na2CO3

C.氯化钠         食盐       NaCl            

D.氢氧化钠      纯碱     NaOH

答案

答案：C

问答题 简答题

如何识别一个文件的类型？什么叫文件关联？文件关联的作用是什么？
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单项选择题

The very ubiquity of electronic communications can have a surprising downside, notes Richard Kohn, a military historian at the University of North Carolina: a wife becomes accustomed to frequent e-mail from her husband, until he can’t get to a computer. And then her anxiety increases.()

A. failure

B. underside

C. drawback

D. consequence
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