单项选择题
Co-operation means working together for the benefit of all. Without co-operation modern society could not exist. Co-operation has at its best among the farmers in the dry areas of certain parts of Australia and Africa. The fields have been irrigated in these areas. Crops cannot be grown without water. For this purpose, canals and reservoirs have been built. The canals have been cut through the fields of not only one farmer. Those who live higher up the valley than the others have permitted canals to be built through their land in order to carry water to the fields of farmers lower down. When there is a long period without rain, all share the water. Instead of taking all the water for themselves, the farmers in the higher land leave enough water for their neighbours down the valley. Farming in the dry areas has been made possible by such co-operation. By co-operation farmers have learned to make even the desert produce crops.
Crops can be produced in desert only because(). A. there is a lot of rain
B. there is one reservoir
C. the people work together for the benefit of all
D. many wells have been found