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问题 选择题

下列关于物质用途不正确的是（　　）

A．SO2可作食品的增白剂

B．高纯硅可制造光电池

C．O3可作自来水的消毒剂

D．Na2O2可作潜艇的供氧剂

答案

A．二氧化硫有毒，则SO2不能作食品的增白剂，故A错误；

B．硅可作为电池板的材料，则高纯硅可制造光电池，故B正确；

C．臭氧具有强氧化性，可作自来水的消毒剂，故C正确；

D．过氧化钠与水或二氧化碳反应生成氧气，则Na2O2可作潜艇的供氧剂，故D正确；

故选A．

单项选择题

College librarian: Until three years ago, nonstudents used the library without charge. Then, because of our decreased budget, they were asked to pay $100 per year. Nevertheless, about 150 nonstudents still use the library without paying. We will therefore gain financially if we hire a guard to identify nonstudents and ensure that they have paid the fee.
Which of the following would it be most important to know in order to evaluate the librarian’s conclusion

A．The number of students who use the library annually.

B．The library’s budget this year.

C．Whether the library has installed an expensive computerized cataloging system.

D．How much the library’s budget was decreased three years ago.

E．(E) The annual cost to the library of hiring a guard.
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单项选择题 B1型题

可治疗带下、阴挺、闭经的是（）

A.解溪

B.梁丘

C.大横

D.归来

E.太白
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