问题 选择题

李海同学骑车上学,因为赶时间经常忘记收起自行车支架便骑车或没有锁车就离开,因此他想设计提醒收支架和锁车的电路.在兴趣小组活动中,他请同学们一道设计提醒锁车的电路,要求:当车的支架支起(开关S1闭合)时,蜂鸣器响起,提醒锁车;当车上锁(开关S2断开)后,蜂鸣器停止发声.他们设计了如图所示的四个电路,其中符合要求的是(  )

A.

B.

C.

D.

答案

A、开关S1闭合时,蜂鸣器被短路,不可能响起,不符合题意.

B、开关S1闭合时蜂鸣器响起,开关S2断开后蜂鸣器停止发声,符合题意.

C、蜂鸣器被S2短路,S1闭合时,蜂鸣器不可能响起,不符合题意.

D、S1未闭合时,蜂鸣器会一直在响,不符合题意.

故选B.

阅读理解

阅读理解。

           Now, China has the second largest number of Internet users in the world after the United States.

 Many of Chinese Internet users are teenagers. They spend about 13 hours every week online. On the

 Internet, students can find out almost anything. Surfing the Internet(网上冲浪)can help them with their

  homework and learn a lot of knowledge.

     People can use the Internet to write letters, stories and to send emails. Many teenagers keep in touch

 with their friends online. They can also make new friends through QQ or ICQ.

     Some of the students surf the Internet just for fun. They like to listen to music, watch films, and go to

 their favourite stars' websites.

     But some parents always think that the Internet takes young people away from study. "They spend too

  much time playing computer games and most games are about killing and fighting. It's too dangerous. And

 there are some dirty things on the Internet, "says the mother of a 13-year-old boy.

1. According to this passage, China has the ______ highest number of Internet users.

    A. second

    B. third

    C. fourth

    D. fifth

2. The phrase"keep in touch with"means ______ .

    A. 浏览网站

    B. 交朋友

    C. 打电话

    D. 保持联系

3. Some of the students surf the Internet for fun. What can they do?

    A. They can listen to music and watch films.

    B. They can go to their favourite stars’ websites.

    C. A and B.

    D. We don't know.

4. Some parents worry that the Internet is ______ .

    A. helpful

    B. dangerous

    C. traditional

    D. useful

5. What's the best title of this article?

    A. The Internet

    B. The Computer

    C. The Teenagers

D. Surfing the Internet

单项选择题