用括号中所给的动词的适当形式填空。
1. You must _____ (look) after your pet dog. Don't let it run here and there.
2. —What's behind the door?
—There _____ (be) two balls.
3. —Why not _____ (sing) an English song together?
— Good idea.
4. There _____ (be) some money in that purse.
5. We are planning _____ (go) for a picnic this Sunday.
6. It often _____ (rain) here in summer.
7. You must remember _____ (close) the window when school is over.
8. The students are busy _____ (do) their homework.
9. _____ (skate) is my favorite sport.
10. There _____ (be)a pen and some books on the desk.
