1 He can't walk very fast because he has hurt a leg.
2.I can't get in because I have lost a key.
3.I know this story very well because I have seen the film.
4. ...because I haven't put a stamp on it.
5. ...because he hasn't eaten too much.
6. ...because they haven't saved money.
7. ...because I have met him before.
8. ...because we haven't heard from him.
9. ...because he has given up smokimg.
10. ...because he has locked the door.