Welcome to the Grand Center--the place for all the family
If you like sports, go to the sports center on the twenty-eighth floor. On the twenty-eighth floor, we have a ping-pong room. If you like films, go to the twenty--seventh floor and watch a film in the ABC Cinema.
If you like to eat, there are a lot of places in the Grand Center for you to go to. You can try Wonderful Restaurant. That’s a new restaurant on the twenty-first floor. Crazy Town ( a Sichuan restaurant)is on the twenty-third floor and there’s an American restaurant on the twenty-sixth. But don’t worry, children ! If you like other kinds of foreign food, you can go to the coffee shop on the first floor. It’s really great.
If you like to shop, there are the twelfth to the nineteenth floors. On the twelfth floor, for example, there’s AST World for computers and computer games. There’s a big store on the fifteenth floor for radios, TVs and CDs. And the nineteenth floor has sports stores and a supermarket.
Where call you do shopping
[A] Between the first and the eleventh floors．
[B] Between the twelfth and the nineteenth floors．
[C] Between the twentieth and the twenty-ninth floors．
And there’s Rose Hall for all you dance people ( for people over 14 years old). That’s on the top floor, of course. You can dance and sing all night.
的小物块处于静止状态，小物块与地面间的动摩擦因数
。从t=0时刻开始，空间加上一个如右图所示的场强大小和方向呈周期性变化的电场，（取水平向右的方向为正方向，
取10m/s2。）求：
