1．She has been working for 20 hours.（改为一般疑问句，并作否定回答）
             she       working for 20 hours?No,              .
2．I've been skating since l was six years old.（对画线部分提问）
                           you been skating?
3．Tom ran for one hour.（用现在完成进行时改写）
      Tom                     for one hour.
4.   We have been learning English for three years．（改为同义句）
      We have been learning English                            .
5.   I started playing tennis when I was seven years old. （改为同义句） 
      I started playing tennis                            seven.