问题 选择题
如图所示,两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R,导轨电阻可忽略不计;MN为放在ab和cd上的一导体杆,与ab垂直,其电阻也为R;整个装置处于匀强磁场中,磁感应强度的大小为B,磁场方向垂直于导轨所在平面(指向图中纸面内);现对MN施力使它沿导轨方向以速度v(如图)做匀速运动;令U表示MN两端电压的大小,则(  )

A.U=vBl,流过固定电阻R的感应电流由b到d

B.U=vBl,流过固定电阻R的感应电流由d到b

C.U=vBl,流过固定电阻R的感应电流由b到d

D.U=vBl,流过固定电阻R的感应电流由d到b

答案

答案:A

阅读理解

阅读理解

     In Britain you're allowed to drive a car when you're seventeen.You have to get a special two-year

driving license before you start.When you're learning,  someone with full license always has to be in the

car with you. You don't have to go to a driving school --a friend can teach you. The person with you

isn't allowed to take money for the lesson unless he's got a teacher's license.

    Before you're allowed to have a full license, you have to take a driving test. You can take a test in

your own car, but it has to be fit for the road. In the test, you have to drive round for half an hour and

then answer a few questions. If you don't pass the test, you're allowed to take it again a few weeks later

if you want to.  In 1970, a woman passed her fortieth test after 212 driving lessons!    ,

    When you've passed your test, you don't have to take it again, and you're allowed to go on driving

as long as (只要) you like, if you're healthy.  Britain's oldest driver was a man who drove in 1974 at

the age of 100.

     Before 1904, everyone was allowed to drive, even children. Then from 1904 car drivers had to have

a license.  But they didn't have to take a test until 1935. In the early days of car driving, before 1978,

cars weren't allowed to go faster than four miles an hour, and someone had to lead the car with a red

flag.

1. Which of the following is NOT necessary for a young man who wants to drive a car alone?

A.  He has to pass a driving test to get a full license.

B. He has to learn to drive in a driving school.

C. He has to get a special two-year driving license.

D. He has to reach the age of 17.

2. A person can't take money for driving lessons unless he            

A. has a full license and a teacher's license

B. has a driving school

C. is good at driving

D. has learned to drive in a driving school

3. In the driving test, one ______ .           

A. must drive his own car

B. has to do some test papers

C. is usually asked to drive on roads for half an hour

D. should have 212 driving lessons

4. The car drivers began to take a driving test in______.        

A. 1878                

B. 1904

C. 1935                

D. 1970

5. The best title for the passage is ______.          

A. Britain Car Drivers

B. Young Men's Driving Licenses

C. Tests for British People

D. Driving License in Britain

单项选择题