Bài 4. Dựa vào từ cho sẵn, viết câu hoàn chỉnh.

1. If/people/ not/ stop/ dumping/ waste/ into/ rivers/,/pollution/ increase/.

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2. If/ polar/ ice caps/ melt/ ,/huge landmasses/ be/ under/ water.

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3. If the air/ in/ city/ be/polluted/ ,it/can/ cause/ people’s/ respiratory/ problems.

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4. If/smog/ be/ frequently/ formed/ in/ city/,/it/ cause/ difficulty/ in/ breathing/ headache/ even/ lung cancer.

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5. If/ carbon monoxide/ concentrate/ in/ great/ amounts/, /it/ be/ harmful/.

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6. The climate/ change/ if/ more trees/ be/ cut/ down/ for/ hardwood/.

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7. If/ we/ not/ control/ pollution/ soon/,/it/ be/ too/ late/.

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8. If/we/ not/ protect/ frontier/,/we/ suffer/ many/ from/ natural/ disasters.

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