题干

今有四种粒子的结构示意图,下列说法正确的是(   )

A:它们表示四种元素

B:②表示的元素在化合物中通常显+2价

C:④表示的元素是非金属元素

D:①④表示的是阳离子

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答案(点此获取答案解析)

B

同类题4

阅读理解

    The question of what children learn, and how they should learn it, is continually being debated and redebated. Nobody dares any longer to defend the old system, the parrot-fashion(way of learning by repeating what others say)of learning lessons, the grammar-with-a-whip(鞭子)system, which was good enough for our grandparents. The theories of modern psychology have stepped in to argue that we must understand the needs of our children. Children are not just small adults; they are children who must be respected as such.

    Well, you may say, this is as it should be, and a good idea. But think further. What happens? “Education” becomes the responsibility not of teachers, but of psychologists. What happens then? Teachers worry too much about the psychological implications(暗示) of their lessons, and forget about the subjects themselves. If a child dislikes a lesson, the teacher feels that it is his fault, not the child's. So teachers worry whether history is “relevant” to modern young children. And do they dare to recount stories about violent battles? Or will this make the children themselves violent? Can they tell their classes about children of different races, or will this encourage racial hatred? Why teach children to write grammatical sentences? Oral expression is better. Sums? Arithmetic? No; real-life mathematical situations are more understandable.

    You see, you can go too far. Influenced by educational theorists, who have nothing better to do than write books about their ideas, teachers leave their teaching-training colleges filled with grand, psychological ideas about children and their needs. They make complicated preparations and try out their “modern methods” on the long-suffering children. Since one “modern method” rapidly replaces another, the poor kids will have well been fed up by the time they leave school. Frequently the modern methods are so complicated that they fail to be understood by the teachers, let alone the children; even more often, the relaxed discipline so necessary for the “informal” feeling the class must have, prevents all but a handful of children from learning anything.