用所给动词的适当形式填空。

1. _____ you _____ (read) this story book before?

2. My mother _____ (go) out .She 's doing shopping in town.

3. The car doesn't move. What _____ I _____ (do)?

4. It was seven in the morning and Li Ping _____(have)some reading at his desk.

5. Let's run and seen who _____ (get) to the finishing line first.

6. Little Tom _____(draw) every evening after supper but he _____ (not draw)

at the moment.

7. "Listen! Who_____ (sing) in the next room?" "Maybe it is Wang Lin. She likes

_____ (sing) a lot."

8. Lucy _____ (not finish) her work yet. She _____ (do) it now. I _____ (be)

sure she _____ (finish) it soon. After she _____ (finish) it ,we _____ (go)

swimming together.

9. The story_____ (happen) many years ago.

10. At night we can always see him _____ (study) in the room .

两物体的重力都为10N，各接触面之间的动摩擦因数均为0.3．A、B两物体同时受到F=1N的两个水平力的作用，如图所示，那么A对B、B对地的摩擦力分别等于

A．2N，0N     B．1N，0N

C．1N，1N    D．3N，6N