51.They will have to change the date of the meeting again
The date of the meeting will have to be changed
52.I don’t have a key, so I can’t get in

 If I had a key I could get in.

53.I’m too poor to take a space trip
I’m not rich enough to take a space trip.
54.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
55.Since he was careless, Tim lost his job
Because of his careness, Tim lost his job
56.Let’s go abroad for our holiday this year
Why don't we go abroad for our holiday this year
57.It’s nearly 20 years since we knew each other
We known each other for 20 years

51.The date of the meeting will have to be changed.
52.If I had a key I could get in.

53.I’m not rich enough to take a space trip.
54.Although she was tired , she stayed up late to watch the late film on TV.
55.Because of his careness, Tim lost his job.
56.Why don't we go abroad for our holiday this year.
57.We known each other for 20 years.