用所给单词的适当形式填空    

1.  It's hard          (stop) riding cars.   

2.  _    ___ ( recycle) paper is really hard.  

3.  The trees can stop the wind          (move) towards the rich land.   

4.  I stopped          (use) napkin last year.   

5.  She remembered              (lock) the door, but she didn't.