Nearly all our food comes from the soil（土地）. Some of us eat meat, of course, but animals live on plants. If there were no plants, we would have no animals and no meat. So the soil is very necessary for life. The top of the ground is usually covered with grass or other plants. There may be dead leaves and dead plants on the grass. The waste matter（粪）from animals also falls on it.
   All soil needs food. If we do not give it any, the plants will be weak. Farmers found that animals' waste is the best food for the soil, but chemical fertilizers（化肥）are also very useful. The same crop（庄稼）should not be grown in the same place every year, it's better to have a different crop. A change of crop and the use of a good fertilizer will keep the land good.

美丽富饶的新疆地区成为我国不可分割的领土，开始于（  ）