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6. Before Nick went to bed last night, he had done his homework.
7. He has to study for his exam, so he can't go out.
8. If he took some exercises, he wouldn't be unhealthy.
9. That he smokes too much leads to some health problems./ His smoking too much leads to some health problems./ He smokes too much, which leads to some health problems.
10. Because it rained heavily, I didn't go to school.
11. If people cared much about environment, they wouldn't keep making it worse.
12. Since she drank contaminated water in a long time, she suffered from a serious disease.
13. If the drainage system weren't damaged, there would be enough water for the crop.
14. Before the house collapsed, the children had left the house.