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
