灰尘,多讨厌!刚擦过的窗玻璃,没几天就不那么明亮了。桌子用抹布擦过,不久就蒙上一层薄薄的灰尘。雪白的衬衣很快就脏了。大晴天,汽车开过马路,往往扬起一股灰尘,行人不得不用手帕、用衣袖蒙住脸,屏住气,免得把灰尘吸进肺里。你可知道:车辆往来卷起的灰尘,工厂的烟囱排出的粉尘,都是污染大气的物质,如果含有铅汞等有毒的金属微粒,会严重地危害人 Dust, how annoying! Just wiping the glass, a few days is not so bright. The table was rubbed with a rag and soon covered with a thin layer of dust. White shirt soon dirty. On a sunny day, the car ran across the street, often raising a cloud of dust. Pedestrians had to use handkerchief to cover their face with their sleeves and hold their breath so the dust would not get into the lungs. As you can see, the dust that comes in from the rolling stock and the dust from the chimney of the factory are all substances that pollute the atmosphere. If it contains poisonous metal particles such as lead and mercury, it can seriously endanger people