1. If I had known she was sick, I would have visited her.
=> Had i known she was sick, i would.....
2. If the train had been delayed, I would have sent the telegram.
=> Had………the train been delayed, i would have....
3. The only reason the party was a success was that a famous film star attended.
=> Had it not……been for the attendence of the famous film star, the wouldn't have succeed
4. The only thing that prevented the passing of the bill was the death of the Prime Minister.
=> Had it not………been for the death of the prime minister, the passing of the bill wouldn't have prevented 
7. Please let me know if you wish to keep the books any longer.
=> Should you wish to keep the book any longer,please lt me know
8. If I were the Prime Minister, I would reduce taxes.
=> Were It the Prime Minister, i would reduce taxes
9. If Marry had given it in on time, she would have got a high mark.
  => Had………marry given it on time, she would.....
10. If John had played for our football team, we would not have lost the game.
=> Unless……john hadn't  played for our football team, we would...
11. If I won a big prize in a lottery, I’d give up my job.
=> Unless………i didn't win a big prize in a lottery, i'd....
12. If you don’t like this one, I’ll bring you another.
=> Unless………you like this one, i'll.....
13. I’ll only help you if you promise to try harder.
=> Unless………you promise to try harder, i won't help you
14. With a bit more help, I would have finished it on time.
=> If ........it had been for your help i would have....
15. Without the help of the Red Cross doctors, many more would have died.
=> If ……it hadn't been for the help of the red cross, many more.....
16. If the train arrives on time, they’ll be here in a few minutes.
=> Assuming ........…the train arrives on time, they’ll be here in a few minutes.
17. You can go out tonight if you get back by midnight.
=> So long as ……you get back by midnight, You can go out tonight
18. If you had a lot of money, do you think you would give up work?
=> Supposing ………you had a lot of money, do you think you would give up work?
19. If Rosie gets this new promotion, we’ll have enough money for a holiday.
=> Provided …......that Rosie gets this new promotion, we’ll have enough money for a holiday
20.  Mr David will give a talk at the conference if we pay him a reasonable fee.
=> On .....condition that we pay Mr David a reasonable fee, he will give a talk at the conference