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_爱下问搜题

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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

完形填空

There are lots of funny stories in my childhood .The first one that 16 my mind is the story of my first camera. It happened 20 years ago . Just when I was ready to go to school , my grandmother 17 me a new camera from the supermarket as a present . Even if my mother wasn’t too happy about what I had 18 , I asked my father if I could take my camera to my 19   so that I could take pictures with my classmates . He agreed and show me how it 20 . It was very easy.
At school I showed it to all my 21 and we took a lot of pictures, 22 they were not too great . The photo with my friends was the worst as I didn’t took Tom’s head ; instead I 23 his sandwich . The boys were interested in my camera ,   24 Daniel who said he had a 25 one with a flashlight . He explained to us that the flashlight helped to take pictures in the 26 but I accused(指责)him of being a liar . Like all boys we started fighting . 27 ,our teacher separated us .After explaining to him the reason of the fight , I   28 him not to take my camera away.
When my parents knew what had happened , they weren’t glad . My mother punished me for being 29   . She took the camera in order to   30 further problems , telling me that for a boy like me the camera was not a good 31   to play with.
To make her 32 about the fight , I took a picture with her and Dad with the film left . In a couple of days Dad 33 the films and brought the photos home , saying I wasn’t good at taking pictures at all . I got 34 and argued that we all learnt from our   35 .

A．breaks into

D．Surprisingly

多项选择题

用作道路基层的整体型材料有( )等。

A.石灰粉煤灰稳定砂砾

B.石灰稳定砂砾

C.石灰煤渣

D.水泥稳定碎砾石

E.泥灰结砾石