15. I don't go to the United States of America, so I don't see a lot of beautiful sights there.
---> If__________.
16. I don't understand the answer, so I can't tell you.
---> If__________.
17. Paul will not get good marks in the examination because he studies lazily.
---> If__________.
18. Ben is not intelligent enough to answer your question.
---> If___________.
19. The student is so tired that he can't go on his study now.
---> If__________.
20. I will go there. I will buy you a dog.
---> If__________.
21. We can't go out because it is raining.
---> If__________.
22. I can't help you because you don't tell me your problem.
---> If__________.
23. We won't have a holiday because we don't have enough money.
---> If__________.
24. Peter doesn't go to the party today because it rains heavily.
---> If__________.
25. You don't speak loudly, he won't hear anything.
---> Unless__________.