下列有关实验现象的描述，正确的是( )_刷题宝

题干

下列有关实验现象的描述，正确的是( )

A：红磷在空气中燃烧产生大量白雾

B：镁条在空气中燃烧发出耀眼的白光

C：铜在空气中加热生成氧化铜

D：CuSO₄溶液与NaOH溶液反应生成白色沉淀

上一题下一题 0.0难度选择题更新时间:2016-04-21 11:58:37

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B

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已知a+b=4，ab=2，则a²+b²=____．

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如图为动、植物细胞结构示意图．请据回答：

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如图所示的电路中，电源电压恒定，R₂=10Ω，开关S、S₁都闭合时，电流表示数为0.4A；开关S闭合，开关S₁断开时，电流表示数变为0.3A．则电源电压为____V，电阻R₁的阻值为____Ω．

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下列词语的书写完全正确的一项是（）

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