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___ fumes from these vehicles are serious air pollutants.

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We saw many beautiful birds while we ____ in the lake.

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____ she left the party, Jenny said goodbye to the host.

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People think that global warming ____ lots of problems in the future.

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Too much use of electric lights in cities may ______ light pollution.

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Land pollution is responsible for damage done ___ natural habitat of animals.

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I learned a lot about wildlife until/ after I visited Cuc Phuong National Park yesterday.