11. I'll call the police if you don't leave me alone.

⇒ Unless you leave me alone, I'll call the police.

12. Many people speak English in the world.

⇒ English is spoken by many people in the world.

13. People get more diseases. The water is contaminated.

⇒ If the water is contaminated, people will get more diseases.

14. David had gone home before we arrived.<CÂU NÀY ĐỀ SAI NHA BN>

⇒ After David had gone home, we arrived.

15. Aquatic life suffers or dies because there is thermal pollution.

⇒ Because of the thermal pollution, aquatic life suffers or dies.

16. You use compact light bulbs. You save a lot of energy.

⇒ If you use compact light bulbs, you will save a lot of energy.

17. They are going to organise a garden party to raise money for the victims of the flood.

⇒ A garden party is going to be organised to raise money for the victims of the flood.

18. The waiter took my plate. I didn't finish eating my meal yet.

⇒ The waiter had taken my plate before I finished eating my meal.

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11. Unless you leave me alone, I'll call the police.
12. English is spoken in the world.
13. If the water weren't contaminated, people wouldn't get diseases.
14. After we had gone home, we arrived.
15. Because the thermal pollution, aquatic life suffers or dies.
16. If you use compact light bulbs, you will save a lot of energy.
17. A garden party is going to be organised to raise money for the victims of the flood.
18. The waiter took my plate before I finished eating my meal.