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:B
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
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.