21.She was tired, but she stayed up late to watch the late film on TV
Although..........She was tired,  she stayed up late to watch the late film on TV
22.Since ha was careless, Tim lost his job
Because of...........being careless, Tim lost his job
23.Let's go abroad for our holiday this year
Why........don't we go abroad for our holiday this year
24.It's nearly 20 years since we knew each other
We........have khown each others for 20 years 
25.It's raining, so we can't have lunch in the garden
If.....it wasn't raining , we could have lunch in the garden

21. Although she was tired, she stayed up late to watch the late film on TV
22. Because of his careless, Tim lost his job
23. Why don't we go abroad for our holiday?
24. We have known each other for 20 years
25. If it was not raining, we could have lunch in the garden