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3. If I were a rich businessman , I could afford to buy an expensive car. 
4. If it hadn't rained last night, I would have gone to the barbecue. 
5. If my parents allowed me to go , I would not have to stay at home. 
III/
1. Happily 
2. Economically 
3. Products 
4. Readers 
5. Necessities 
VI/
1. I told a joke, but nobody laughed. 
2. You must study harder, or you will go into another class. 
3. The city suffers from air pollution and water pollution. 
4. I knew her family, so I did what I could for her. 
5. We can't afford energy - saving light bulbs because the light bulbs are too expensive.
V/
1. Learned 
2. Don't have 
3. Attend 
4. Will die 
5. Doesn't have 
VI/
1. After 
2. On
3. For
4. Off
5. On
6. Away
7. In
8. Up
9. Up
10. Off