Sure! Here’s a rewritten version of the sentences using conditional structures:

1. If it is raining heavily, he will fail the exam.
2. If she gets paid tonight, she will have enough money to buy some clothes.
3. If you smoke too much, your health will be weak.
4. If Tuan were more outgoing, he would enjoy the party.
5. If I have a lot of homework tomorrow, I will stay home to do it.
6. If my friend took more exercises, he wouldn’t be so weak.
7. If we woke up earlier, we wouldn’t be late for school.
8. If you study hard, you won’t fail the exam.
9. If you are patient, you will make fewer mistakes.
10. If I had eaten lunch, I wouldn’t have felt hungry.
11. If it hadn’t rained heavily, we wouldn’t have stayed home last Sunday.
12. If you wanted my advice, I wouldn't do that.
13. If you invite her, she will come.
14. Unless she revises all her lessons, she won’t pass the exam.
15. If she had revised her lessons, she would have passed the exam.