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问题 选择题

合金有许多特点，如Na-K合金为液体，而Na和K的单质均为固体，据此试推测生铁、纯铁、碳三种物质中，熔点最低的是 [ ]

A．纯铁

B．生铁

C．碳

D．无法确定

答案

答案：B

单项选择题

A student conducts an experiment in biology lab and discovers that the ratio of the number Of insects in a given population having characteristic X to the number of insects in the population not having characteristic X is 5:3, and that  of the insects having characteristic X are male insects. What proportion of the total insect population are male insects having the characteristic X ？（）

A.A

B.B

C.C

D.D

E.E
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选择题

具有下列结构示意图的微粒，既可以是原子，又可以是阴离子，还可以是阳离子的是

A．

B．

C．

D．
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