用所给词的适当形式填空。
1. When the car (invent)?
2. What do you think (be ) the most helpful invention?
3. A stranger was seen (go) into the teacher's office by the girl.
4. Knocking into players and falling down would be . (danger)
5. I am (save) my money so I can buy a new bicycle.
6. (be) a volunteer is great.
7. I fix up bikes and give (they)away to children.
8. I love places where the people are really (friend)
9. I love singers (whom) write their own music.
10. Teenagers should (allow) to choose their own clothes.