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问题 问答题

右图是远距离输电的示意图，下列说法正确的是（　　）

A．a的输出电压等于b的输入电压

B．a是升压变压器，b是降压变压器

C．a是降压变压器，b是升压变压器

D．a的输出电压等于输电线上损失的电压

答案

因电路导线有电阻，会有电压损示，故a的输出电压要大于b的输入电压．且a的输出电压减去输电线上的损失电压等于B的输入电压，故A错误，D错误；

     因能量损失与输送电压的平方成反比故为减小电路能量损耗，要用高压送电，到用户要进行降压．故B正确；C错误

故选：B

单项选择题

磁盘存储器的数据存取速度与下列哪一组性能参数有关 ( )。

A．平均等待时间，磁盘旋转速度，数据传输速率
B．平均寻道时间，平均等待时间，数据传输速率
C．数据传输速率，磁盘存储密度，平均等待时间
D．磁盘存储器容量，数据传输速率，平均等待时间
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单项选择题

Like all the huge metropolises of the world, there are lots of diversions both outdoors and indoors in Chicago. The Art Institute of Chicago has one of the world’s (1) art collections, including more French Impressionist paintings than even in the Paris Louvre itself. The Field Museum of Natural History and the Museum of Science and Industry are also great historical and cultural treasure houses to (2) as well as entertain children and adults (3) In the Field Museum one comes (4) a surprisingly big collection of Chinese exhibits from the ancient (5) to the early century. The Sears Tower and the Buckingham Fountain are the pride of the Chicagoans; (6) having 110 storeys is said to be the highest tower in the world and the (7) is the largest fountain in the United States. Lake Michigan is for yachting in summer time, (8) the highlights of Chicago life all the year round are concerts, operas and plays (9) by the city’s orchestra, opera houses and theatres. In summer, especially around the Independence Day, July 4th, many festivals and fairs are given outdoors, which, (10) crowds and crowds of people, with their parades, fireworks, (11) concerts, water-skiing and good foods.

But with all its attractions and beautiful spots Chicago is also a city (12) for crimes. All the dwelling houses are (13) with three doors and visitors have to speak through microphone (14) in the wall to the residents before they can get admitted. In the streets there are white-color telephones. When one finds oneself (15) , he needs only to knock the receiver (16) the hook and the next instant the police will (17) . If one does not drive a car, it may well be dangerous for him or her to go out alone in the evening. At first I did not take this warning seriously. (18) , my two encounters with the Black people (19) dusk in the neighborhood were so unpleasant and frightening that I have (20) shut myself evenings in my room, in almost all studying, imposing a curfew on myself.

16（）

A.off

B.out

C.down

D.away
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