A:百姓不再是封君的属民
B:由血缘政治转向地缘政治
C:中央集权政治开始出现
D:由贵族政治转向官僚政治
The firemen know _____ to do.
— 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.