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[重点词组或短语]1.at the bottom of the river在河床底部2.be full of rubbish充满了垃圾3.throw litter into the river把垃圾扔入河中4.play a part in cleaning it up尽一份力把它清理干净5.land pollution土地污染6.fill the air with black smoke空气中充满黑烟7.cut down air pollution减少空气污染8.make a difference产生影响