1. he can't walk very fast because he has hurt his leg.
2. i can't get in because i have lost my keys.
3. i know this story very well because i've seen the film.
4. i can't post the letter because i haven't put a stamp on it.
5. he can't stand up because he has eaten too much.
6. they can't go on holiday because they haven't saved money.
7. i know him because i've met him before.
8. we don't know how he his because we haven't heard from him.
