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V/
1. He couldn't meet you because he was busy.
2. She went to bed early because she was sick.
3. Nobody can do this test because it is difficult.
4. Two cars can't pass each other because the road is narrow.
5. We spent the whole day in the garden because the weather was lovely.
6. He can't go to school today because he has a toothache.
7. I can't play basketball because I am short.
8. She must stay in bed because she is ill.
9. We can't swim in this part of the river because the water is highly polluted.
10. They couldn't keep on cleaning the beach because it rained heavily.
VI/
1. If you are late again, you will lose your job.
2. I can't see anything because it is dark.
3. His parents are happy because he gets a good job.
4. My dog always barks if it hears any strange sound.
5. She was late for work because she missed the bus.
6. She doesn't work hard because of being old./She doesn't work hard because she is old.
7. If my homework were not long and difficult, I would finish on time.
8. She can't read books because she doesn't have enough time.
9. We didn't go for a walk because it rained heavily.
10. If people stop using dynamite for fishing, (a lot of) sea creatures will be well preserved.