如图所示的电路中，电源电压是8V，一个最大阻值为50Ω的滑动变阻器与一个阻值是50Ω的电阻串联后，闭合开关S。当滑片P从
向
移动的过程中，电压表示数的变化范围是
A．0.8V
B．8V～3V
C．0V～4V
D．4V～8V
D
由电路图可知，定值电阻和滑动变阻器串联·电阻越大，分压越多，当触头在"端时，V示数最小，最小值为U =4V，当触头在b端时，V示数最大, 最大值为U=8V，故变化范围是4V-8V.
| 完形填空 阅读下面短文，掌握其大意，然后从每题所给的A、B、C、D 四个选项中选出可以填入空白处的最佳选项。 | |||
| Everyone needs friends. But do you know1 to find real friendship and keep it? An American writer 2 Sally tells young students some good ways to find 3 .Sally says finding friendship is just like 4 a tree. You plant the seed（种子）and 5 it to make it grow. She says you should first choose someone 6 can be a good friend. It doesn’t matter whether he has money or good looks. A good friend should be kind and7 . If you have a bad day, a good friend should 8 your complaints（抱怨）and do his 9 to help you. If you want to make a friend, you should make each other 10 . But things cannot always be happy. 11 the best friends may have quarrels（争吵）. What should you do when you 12 with your friend? You may try to have an honest talk with him when there is no one around. If he 13 want to talk, you can write a letter to tell him how you are feeling. Sally also tells us some small but important things, 14 example, celebrating your friend’s success. Remember that friendship is the 15 important thing in your life. Life is great if you have friends! | |||
| ( )1. A. how ( )2. A. call ( )3. A. girls ( )4. A. watering ( )5. A. take off ( )6. A. what ( )7. A. beautiful ( )8. A. look at ( )9. A. good ( )10. A. happy ( )11. A. Even ( )12. A. talk ( )13. A. doesn't ( )14. A. to ( )15. A. too | B. what B. calls B. teachers B. planting B. take away B. which B. helpful B. look B. well B. happily B. Though B. talks B. don't B. for B. much | C.when C.name C.friends C.cutting C.take care C.whose C.thankful C.listen to C.better C.unhappy C. If C. quarrel C. didn't C. in C. more | D. which D. named D. classmates D. decorating D. take care of D. who D. wonderful D. listen D. best D. unhappily D. Ever D. quarrels D. isn't D. at D. most |