甘肃省2012届高三英语二轮专题集训：补全对话+单词拼写（26）补全对话：根据短文内容，从短文后的选项中选出能填入空白处的最佳选项，选项中有两项为多余选项。 m: do you know something about pollution? w: 1 m: what kinds of pollution have you learned about? w: 2 m: where does air pollution come from? w: 3 m: what is it caused by? w: 4
