1. They don't understand the problem. They won't find a solution​
=> If they understood the problem, they’d find the solution.
2. Go right now or you'll be late for the train.
=> If you don’t go right now, you’ll be late for the train.
3. Because you speak English unnaturally, they do not understand you.
=> If you spoke English naturally, they’d understand you.
4. We didn't know your phone number, so wee could not contact you.
=> If we had known your phone number, we could have contacted you.
5. Because Simon doesn't live near his mother, he can't visit her often.
=> If Simon lived near his mother, he could visit her often.
6. She didn't hurry, so she missed the train.
=> If she had been hurry, she wouldn't have missed the train.
7. John is fat because he eats so many chips.
=> If John didn't eat so many chips, he wouldn't be fat.
8. Bill never does anything if you don't tell him what to do.
=> Unless you tell him what to do, Bill never does anything.
9.They don't have enough time so they cannot do me a favour.
=> If they had enough time, they could do me a favour.
10. I must leave now, or I'll miss the flight.
=> If I don't leave now, I'll miss the flight.
11. Hurry up, or we will be late for the exam.
=> If we don't hurry up, we will be late for the exam.
12. Peter gets bad marks because he doesn't prepare his lesson well.
=> If Peter prepared his lessons well, he wouldn't get bad marks.
13. He doesn't apply for the job because he doesn't have enough qualifications.
=> If he had enough qualifications, he would apply for the job.
14. We can't buy this car because it is very expensive.
=> If it weren't very expensive, we could buy this car.
15. Unless he phones her immediately, he won't get any information.
=> If he doesn't phone her immediately, he won't get any information.