1. 用给单词的适当形式完成句子

1. （1） We should do our best (save) trees.

3. （2） There are (million) of stars in the sky.
   

5. （3） He is a strong (fight) for the right(权利) of the children.
   

7. （4） There are many kinds of (gas) in the air.
   

9. （5） I spent the morning (dig) in my garden.
   

11. （6） When the teacher came in, the student stopped (talk).
    

13. （7） — Why can't these trees grow in the north?
    

      — Because cold weather is (harm) to them

15. （8） Can you tell me when (plant) the tree?
    

17. （9） Many (live) things will lose their homes because of deforestation.
    

19. （10） We can use trees (make) paper, so trees are important to us.