B) 阅读下面的短文，根据首字母的提示在空白处填上适当的单词，使短文意义完整。(For questions 71—80, read the passage below. Complete it by filling in each blank one word. The first letter of each word is provided.)

The Home of the Future

When Dan Green comes home from work, he doesn't need a key to open his front door. As he walks up to the front of his house, the (71)d________ opens. The lights turn on inside. His favorite music starts to play. His dinner is (72)r________ in the oven. (73)B________ no   one   is   home.   What's happening? This is the home of the future! Right now, Dan Green is the  only  person (74)w________ has a home like this. He is a scientist. But  in  about  25 years, many  people (75)w________ have homes like Dan's. His  home  does  not  look different on the (76)o________. But inside it is very different.

Computers control this house of the  future. For (77)e________, Dan  is  watching  television  (78)w             the doorbell rings. The TV is a computer. When Dan presses a button on the TV remote control, he can see  a picture of his (79)v________ on  the  screen. He  can  also  use  the remote control to open or close the door. Dan can watch TV and answer the door at the same   (80)t________.

如图所示，质量为m的木块压缩轻质弹簧静止在O点，水平面ON段光滑，长为L的NN/段粗糙，木块与NN/间的动摩擦因数为．现释放木块，若木块与弹簧相连接，则木块最远到达NN/段中点，然后在水平面上做往返运动，且第一次回到N时速度大小为v；若木块与弹簧不相连接，木块与弹簧在N点即分离，通过N/点时以水平速度飞出，木块落地点P到N/的水平距离为s．求：

（1）木块通过N/点时的速度；    

（2）木块从O运动到N的过程中弹簧弹力做的功；  

（3）木块落地时速度vp的大小和方向．