=>
4. If I hadn't felt tired, I could have played football this afternoon. 
5. If Olga and Ivan had been paying attention, they would have seen the sign marking their exit from the highway. 
6. If she had a college degree, she could be employed. 
7. If she hadn't walked to the meeting, she wouldn't have been late. 
8. If you don't promise to return back, I won't lend you. 
9. If the weather hadn't been terrible, we wouldn't have put off our trip. 
10. If Sally hadn't been absent from school on Friday, she would know what she has to do for homework. 
11. Unless you like this one, I'll bring you another. 
12. But for Martin's nerve, he wouldn't have failed the driving test last week. 
13. If he pays me tonight, I will have enough money to buy a car. 
14. If you don't leave me alone, I'll call the police. 
15. Should you arrive at the office earlier than I do, please turn on the air - conditioner.
16. Had it not been for his early death, he would be a famous musician by now. 
17. Were you to take good care of the car, it wouldn't break down so often. 
18. If you tell lies to your boss, you'll be fired at once. 
19. Had he revised all his lessons, he wouldn't have failed the exam.