24. – Is that book worth______?　 -- Yes, it is worthy ______ twice.

　A. reading; being read　　 B. to read; to be read

C. of being read; reading　　 D. reading; of being read

23. Only when your identity has been checked, ______.

　A. you are allowed in　 B. you will be allowed in

　C. you will allow in　 D. will you be allowed in

22. The villagers were almost completely _____ from the outside world after a heavy snow.

　A. cut out　　 B. cut off　 C. cut up　　 D. cut through

21. The listeners got _____ at the _____ speech by the famous scientist.

　A. exciting; excited　 B. exciting; exciting　 C. excited; excited　　 D. excited; exciting

20. Nobody will be _____ about what he eats in time of great hunger.

　A. special　　 B. strange　　 C. particular　　 D. bored

19. Mr Read made up his mind to devote all he had to _____ some schools for poor children.

　A. set up　 B. setting up　 C. have set up　　 D. having set up

从所给A、B、C、D选项中，选出可以填入空白处的最佳选项。

18.　 It was ______ of you not to turn on the radio while I was writing my paper.

　A. considering　 B. considered　 C. considerate　　 D. consideration

18.(09年广东物理)(15分)如图18(a)所示，一个电阻值为R ，匝数为n的圆形金属线与阻值为2R的电阻R₁连结成闭合回路。线圈的半径为r₁ . 在线圈中半径为r₂的圆形区域存在垂直于线圈平面向里的匀强磁场，磁感应强度B随时间t变化的关系图线如图18(b)所示。图线与横、纵轴的截距分别为t₀和B₀ . 导线的电阻不计。求0至t₁时间内

(1)通过电阻R₁上的电流大小和方向；

(2)通过电阻R₁上的电量q及电阻R₁上产生的热量。

解析：⑴由图象分析可知，0至时间内　

由法拉第电磁感应定律有

而

由闭合电路欧姆定律有

联立以上各式解得

通过电阻上的电流大小为

　由楞次定律可判断通过电阻上的电流方向为从b到a

⑵通过电阻上的电量

通过电阻上产生的热量