地球同步卫星到地心的距离r可由求出，已知式中的单位是，的单位是，的单位是，则（　　）

A．a是地球半径，b是地球自转的周期，c是地球表面处的重力加速度

B．a是同步卫星轨道半径，b是同步卫星绕地心运动的周期，c是同步卫星的加速度

C．a是赤道周长，b是地球自转周期，c是同步卫星的角速度

D a是同步卫星轨道半径，b是同步卫星运动的周期，c是地球表面处的重力加速度

用所给动词的适当形式填空。

1. How often             your mother              (go) shopping?

2. Peter              (go) to watch the basketball match if he is free tomorrow.

3. Linda              (visit) the Science Museum next Sunday.

4. Mr Huang              (teach) us English two years ago.

5. Mr Green              (live) in Beijing since he came to China.

6. The Kings              (watch) TV at this time last night.

7. Tony will come to my birthday party if it             (not rain) tomorrow.

8. My cousin is a student and he             (study) at a middle school nearby.

9. My father              (be) to Beijing three times this year.

10. Listen! Who              (play) the piano in the next room?