III. Viết lại các câu sau, dùng câu điều kiện loại 2.
1. The river is full of contaminants so many aquatic species are in danger.
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2. Because some students keep littering, the school playground is dirty.
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3. We burn oil and coal for energy so global warming occur.
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4. The tiger populations are on the decline because this species is overhunted for skin and bones.
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