1). He can't walk very fast, because he has hurt his leg.
2).I can't get in, because I have lost my key.
3). I know this story very well, because I have 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 have met him before.
8). We don't know how he is,because we have not heard from him.
9). He won't take a cigarette,because he has gave up smoking
10). She can't get in,because he has locked the door.