下列说法中正确的是（ ）
A．电动机的工作原理是电磁感应现象
B．奥斯特实验说明了电流周围存在磁场
C．电动机工作时，将其他形式能转化为电能
D．发电机是把电能转化为机械能的机器
A、电动机的工作原理是利用通电导体在磁场中受力转动，不是电磁感应现象，故A错误；
B、奥斯特将通电导线放于小磁针上方时发现小磁针发生了偏转，说明了通电导线周围存在着磁场，故B正确；
C、电动机工作时，将电能转化为机械能，故C错误；
D、发电机利用电磁感应来工作的，是把机械能转化为电能的，故D错误；
故选B．
| 阅读理解。 | |||
Welcome to the zoo!
| |||
| 1. On Sunday, the zoo opens at _____. | |||
| A. 10:00 in the morning B. 8:00 in the morning C. 6:00 in the afternoon D. 8:00 in the afternoon | |||
| 2. The zoo opens _____ day(s) a week. | |||
| A. one B. two C. five D. seven | |||
| 3. You are 13 years old. If (如果) you want to go to the zoo, you should (应该) pay (付钱) _____. | |||
| A. ＄3.00 B. ＄6.00 C. ＄8.00 D. ＄2.00? | |||
| 4. Kate is 12 years old, and her little sister is six years old. If they go to the zoo, they should pay _____. | |||
| A. ＄9.00 B. ＄11.00 C. ＄6.00 D. ＄3.00 | |||
| 5. You are 14 years old and your brother is 7 years old. You are going to try the train ride, you should pay _____. | |||
| A. ＄2.00 B. ＄4.00 C. ＄6.00 D. ＄7.00 |