问题 选择题

在右图所示电路中,AB两端电压稳定,当K断开时,则各表读数将(  )

A.A1变小,A2变小,V变小

B.A1变大,A2变小,V变小

C.A1变小,A2变大,V变大

D.A1变大,A2变大,V变小

答案

答案:C

题目分析:根据“并同串反”,当K断开时,R2所在支路电阻增大,R3、V与R2并联,则电压表求数增大,A2求数变大;A1与R2等效串联,则A1求数减小,C正确。

阅读理解

阅读理解。

                     

     It is said that as the population of a city grows, so do its problems. Pollution, too many cars, and crowded

streets are just a few of these difficulties. One way to help with these problems is city trains. Trains traveling

to different parts of a city mean fewer cars and buses on our roads, cleaner air, and more open streets. In

recent years, cities such as Guangzhou, Shenzhen and Shanghai have all built city train lines.   

     The first city train line in China was built in Beijing. The oldest part of the train line, from Beijing Zhan to

Ping Guo Yuan was opened in 1969. Its length was 23.6 kilometres. As the city grew after 1980, so did the

need for more trains. A newer train line was built to help move people around the city centre. The 16-kilometre-

long "circle (环形) line" was finished in 1987. Since that time even more train stations have been built and today

the train lines in the city are over 50 kilometres long.   

     For the 2008 Olympic Games, the trains of Beijing will be very important. It is thought that most of the

people who go to watch the different sports during the Games will travel using trains.

1. The passage tells us about _____.

A. the problems in big cities

B. city trains

C. the history of Beijing

D. 2008 Olympic Games

2. How long was the first train line in Beijing?

A. About 16 kms.

B. About 23 kms.

C. About 33 kms.

D. About 50 kms.

3. In 1977, which of the following places in Beijing could you go to by train?

A. Chao Yang Men.

B. An Ding Men.

C. Che Gong Zhuang.

D. He Ping Men.

4. Which of the following is true?

A. In 2008, the Beijing train line will be nearly 40 years old.

B. The larger population a city has, the fewer problems it faces.

C. More and more cities are building undergrounds for the 2008 Olympic Games.

D. There are 20 stations on the "circle line" in Beijing.

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