问题 选择题
如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力的带电粒子从坐标原点O处以速度v进入磁场,粒子进人磁场时的速度方向垂直于磁场且与x轴正方向成120°角,若粒子穿过y轴正半轴后在磁场中到x轴的最大距离为a,则该粒子的比荷和所带电荷的正负是(  )

A.,正电荷

B.,正电荷

C.,负电荷

D.,负电荷

答案

答案:C

选择题
完形填空

IV.完形填空(共10小题,每小题2分,满分20分)

Tom and Fred were talking about the year 2050.“What will __21___ be like in the year 2050 ?” asked Tom . “I don’t know ,” said Fred . “What do you think ?” “Well , no one knows . But it is ___22___ to guess ,” said Tom . “In the year 2050 everybody will ___23___ a pocket computer.The computer will give people the __24___ to all their problems . We shall all have telephones in our pockets , ___25___ . And we’ll be able to talk to our friends all over the world . Perhaps we’ll be able to __26___ them at the same time . Machines will do ___27___ work , and people will have more ____28____ , perhaps they will work only two or three days a week . They will be able to fly to the moon by spaceship and spend their holidays there .” 

“I’m very ___29___ to hear that . I hope to fly to the moon . And I hope I’ll be able to live ___30___ ,” said Fred . “Won’t that be interesting ? Just like a fish .” 

21. A.our home         B.the traffic           C.a factory              D.the world

22. A.pleased           B.no use             C.interesting             D.unusual

23. A.carry             B.bring             C.give                  D.send

24. A.news             B.ways              C.things                D.answers

25. A.either           B.again               C.too                  D.also

26. A.call              B.see                C.look                 D.listen

27. A.more             B.many              C.lot                   D.every

28. A.work             B.duty               C.holidays              D.times

29. A.sorry             B.glad               C.sure                D.afraid

30. A.in the sea         B.on land           C.on the mountain       D.under the ground