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1. If I knew enough about the machine, I could mend it myself.
2. If Nick had a map, he could find the way.
3. If Tom didn't ignore Lucy, she wouldn't get angry at him.
4. If you throw a stone to water, it sinks.
5. If he had had money, he could have bought that house.
6. If you don't study harder, you will fail the exam.
Unless you study harder, you will fail the exam.
7. If I had known Jane was ill, I would have come to see her.
8. If Tom hadn't helped me, I would have been in bad troubles.
9. If I had a motorbike, I would not travel to work by bus.
10. If he had done much exercise, he would not have failed the exams.
11. If I buy that book, I will give it to you.
12. If we had hurried, we wouldn't have missed the train.
13. If he hadn't been lazy, he would not have failed the examination. 
14. If Jack saw the sight, he could tell you about that.
15. If he didn't drive carelessly, he would not have a serious accident.

16. Unless he hurries, he will be late for school.
17. If it doesn't stop raining, we won't go out.
18. Unless you are patient, you won't get successful.