1:He's done his homework since i came here
-> he did his homework before i came here
2:tom went to scotland last friday anh is still there
->tom had a scotland trip last Friday he was still there.
3:my aunt has been teaching english for 40years.
->my aunt taught English 40 years ago
4:she learnt english when she was 10 years old
->She has been learning English since she was 10 years old