A、B B、Get rid of dust. C、Burn waste paper. D、Screen earth and sand. A可以听到：Garbage from food call be changed into fertilizer．But

Many large cities are anything but beautiful. Streets are littered with trash. In this trash, however, there is still something that can be useful.
    If people want to solve the problem of waste, there is no time to be lost. They must work out ways of making use of good things which are just thrown away as waste.
    When a car gets too old, it may not run any more. But the metal that the car was made of is still good. It can be put to use again. When a bottle is empty, it goes out in the trash. But bottle glass can be ground into sand and used to pave streets.
    Garbage from food can be changed into fertilizer. But first you have to fish out all the glass and metal.
    Garbage can also be a good source for making building blocks, which are then covered with concrete. Now, more and more machines are designed for this purpose. Some day, people will watch films in a magnificent cinema which has been built out of garbage. Future buildings, roads, and cities may be made from garbage. But so far, building beautiful cities out of garbage is only a dream.