材料一：元朝中央机构示意图

材料二：自封建变为郡县，有天下者，汉隋唐宋为盛，而幅员之广，咸不逮元。

材料三：元宣政院印

材料四：澎湖岛分二十有六，巨细相同…．至元间，立巡检司，以周岁额办盐课。

——（元）汪大渊《岛夷志略》

— Air quality in our city is becoming worse and worse.
—Yes. These days' PM2.5 readings are frightening. We must do something to ______air pollution.