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问题 选择题

下列反应中，水作为氧化剂的是（　　）

A．2Na+2H2O=2NaOH+H2↑

B．2F2+2H2O=4HF+O2

C．CaO+H2O=Ca（OH）2

D．Cl2+H2O=HCl+HClO

答案

A．Na元素的化合价升高，水中H元素的化合价降低，水为氧化剂，故A选；

B．F元素的化合价降低，水中O元素的化合价升高，水为还原剂，故B不选；

C．没有元素的化合价变化，不是氧化还原反应，故C不选；

D．只有Cl元素的化合价变化，水既不是氧化剂也不是还原剂，故D不选；

故选A．

多项选择题

一般来说，发生债务危机的国家具有的特征有（）。

A.出口不断萎缩

B.外汇主要来源于举借外债

C.大多数债务国缺乏外债管理经验

D.外债投资效益高，创汇能力强

E.国际债务条件对债务国不利
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单项选择题

Teachers need to be aware of the emotional, intellectual, and physical changes that younga-duhs experience. And they also need to give serious (91) to how they can best (92) such changes. Growing bodies need movement and (93) , but not just in ways that emphasize competition. (94) they are adjusting to their new bodies and a whole host of new intellectual and emotional challenges, teenagers are especially self-conscious and need the (95) that comes from achieving success and knowing that their accomplishments are (96) by others. However, the typical teenage lifestyle is already filled with so much competition that it would be (97) to plan activities in which there are more winners than losers, (98) , publishing newsletters with many student-written book reviews, (99) student artwork, and sponsoring book discussion clubs. A variety of small clubs can provide (100) opportunities for leadership, as well as for practice in successful (101) dynamics. Making friends is extremely important to teenagers, and many shy students need the (102) of some kind of organization with a supportive adult (103) visible in the background.
In these activities, it is important to remember that young teens have (104) attention spans. A variety of activities should be organized (105) participants can remain active as long as they want and then go on to (106) else without feeling guilty and without letting the other participants (107) This does not mean that adults must accept irresponsibility. (108) , they can help students acquire a sense of commitment by (109) for roles that are within their (110) and their attention spans and by having clearly stated rules.

A．off

B．down

C．out

D．alone
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