按要求写出单词的变化形式

1.lead（过去式）__________             

2. impossible（反义词）____________     

3. perhaps（同义词）______________   

4. encourage（名词）____________     

5. cycle（名词）___________          

6.certain（副词）_____________

7. time（形容词）____________         

8. slap（现在分词）_______________

9. space（同义词）____________        

10. sell（名词）_______________