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题文

焊接金属时,能用作保护气的一组气体是( )

A.H2、N2 B.N2、O2 C.CO2、CO D.N2、Ar
科目 化学   题型 选择题   难度 中等
知识点: 空气中常见酸碱盐的质量或性质变化及贮存法
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