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问题 填空题

根据下列实验回答问题．

（1）A实验说明水是由______组成的．

（2）B实验中的主要现象是______．

（3）C实验说明白磷燃烧需要______ 和______条件．

（4）D中发生反应的化学方程式为______，

（5）E实验说明CO2具有______ 和______性质．

（6）F实验可说明______．

答案

（1）A实验是电解水的实验，生成了氢气和氧气，说明水是由氢元素和氧元素组成的；

（2）B实验中是镁与稀盐酸的反应，主要现象是剧烈反应，并有大量气泡生成；

（3）在C实验中，由水中白磷不燃烧而铜片上的白磷能燃烧，说明了白磷燃烧需要与氧气接触，由铜片上的白磷能燃烧而红磷不能燃烧说明了白磷燃烧需要温度达到白磷的着火点；

（4）在D中红磷燃烧生成了五氧化二磷，反应的方程式是：4P+5O2

 点燃 
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2P2O5；

（5）在E实验由下面的蜡烛先熄灭，上面的蜡烛后熄灭．说明了二氧化碳密度比空气大，不燃烧也不支持燃烧；

（6）在F中由黄铜在纯铜上刻划能留下刻痕，说明了黄铜比纯铜的硬度大．

故答为：（1）氢元素和氧元素；（2）剧烈反应，并有大量气泡生成；（3）与氧气接触，温度达到白磷的着火点；（4）4P+5O2

 点燃 
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2P2O5   （5）密度比空气大，不燃烧也不支持燃烧；（6）黄铜比纯铜的硬度大

选择题

从显微镜的目镜中我们看到“p” 字，在玻片标本上是（   ）

A．b

B．p

C．q

D．d
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问答题

Man first appeared on earth about 2 million years ago. Then he was little more than an animal; but early man had a big advantage over the animals. He had in his brain special groups of nerve cells, not present in animals, that enabled him to invent a language and use it to communicate with his fellow men. 46) This ability to speak was of great value because it allowed men to share ideas, and to plan together, so that tasks impossible for a single person could be successfully undertaken by intelligent team-work. Speech also enabled ideas to be passed on from generation to generation so that the stock of human knowledge slowly increased.
It was this special ability that put men far ahead of other living creatures in the struggle for existence. 47) He mastered darkness first with dim lights and later with brighter and brighter lamps, until he can now make for himself so dazzling a light with an arc lamp that, like the sun, it is too p for his naked eyes.
48) Man found that his own muscles were too weak for the work which he wanted to do; he explored many other forms of power until now he has his hands on the ultimate source of physical energy, the nuclear power. From man’s earliest days the flight of birds has raised his wonder and desire. Why should he not fly as they did Then he began to experiment. At last he learnt how to make the right machines to carry him through the air. Now he can fly faster than sound. Already he has plans for conquering space, and a series of experiments has been completed. 49) It will not be long now before man takes a giant step away from his planet and visits the moon, learning what it is like to have no weight to his body, no upward direction and no downward.
Man, always a wanderer, has to overcome the difficulty of adapting himself to different climates. 50) Fortunately, in spite of having no thick skin or warm fur to protect him, he is peculiarly p compared with other living creatures, most of whom are unable to live far outside the region that suits them best.
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