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问题 选择题

关于氧化还原反应的说法中正确的是（　　）

A．氧化还原反应的本质是电子得失或偏移

B．失去电子的物质是氧化剂

C．原子得到电子后，元素的化合价一定升高

D．化合反应一定是氧化还原反应

答案

A．化学反应中，当有电子得失或偏移时，发生氧化还原反应，为氧化还原反应的实质，故A正确；

B．失去电子的物质，所含元素的化合价升高，被氧化，为还原剂，故B错误；

C．原子得到电子后，元素的化合价降低，故C错误；

D．化合反应不一定是氧化还原反应，如Na2O+H2O=2NaOH，各元素的化合价都没有发生变化，不是氧化还原反应，故D错误．

故选A．

问答题

如图所示，质量为m的带电小物体，以某一初速度从A点出发，在绝缘水平面上沿直线ABCD运动．已知AB间距离为l1，BC间距离为l2，AC段的动摩擦因数为μ，CD段是光滑的，物体在BC段上运动时还受到竖直向下的电场力Fe的作用，其大小为

1
2
mg．求

（1）物体m至少具有多大的初速度，物体才能达到CD区域；

（2）若物体m到达C点刚好停止，则从B点运动到C点所需要的时间t．
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填空题

A good translator is by definition bilingual. The opposite is not ______(1) true, however. A born and bred bilingual will still need two__________(2) to become a translator: first, the skills and experience necessary for__________(3); second, knowledge of the field in which he or she will__________(4). The skills and experience for translation include the ability to write ______(5) in the target language, the ability to read and understand the_________(6) language material thoroughly, and the ability to work with the latest__________(7) and communication hardware and software.Does a born and bred bilingual__________(8) a better translator than someone who learned language B later in__________(9) There is no definite answer, but the following issues are important.__________(10), a born and bred bilingual often suffers from not truly knowing __________(11) language well enough to translate, with some even suffering from what __________(12) known as a lingualism, a state in which a person lacks_________(13) full, fluent command of any language. Second, born and bred bilinguals__________(14) don’’t know the culture of the target language well enough to_________(15) top-quality translations, or cannot recognize what aspects of the source language__________(16) its culture need to be treated with particular care, as they_________(17) in a sense too close to the language. And last, they often_________(18) the analytical linguistic skills to work through a sticky text.On_________(19) other hand, the acquired bilingual may not have the same in-depth _________(20) of colloquialisms, slang, and dialect that the born bilingual has. Also, the acquired bilingual will not be able to translate as readily in both directions (from B to language A and A to language B). Finally, born bilinguals often have a greater appreciation of the subtleties and nuances of both their languages than someone who learns their B language later in life can ever hope to have.
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