Passage Four
Water problems in the future will become more intense and more complex. Our increasing population will tremendously increase urban wastes, primarily sewage. On the other hand, increasing demands for water will decrease the amount of

Passage Four
Water problems in the future will become more intense and more complex. Our increasing population will tremendously increase urban wastes, primarily sewage. On the other hand, increasing demands for water will decrease the amount of water available for treating wastes. Rapidly expanding industries which involve more and more complex chemical processes will produce larger volumes of liquid wastes, and many of these will contain chemicals which are poisonous. To feed our rapidly expanding population, agriculture will have to be intensified. This will involve ever-increasing quantities of agricultural chemicals. From this, it is apparent that measures must be taken immediately to develop corrective measures for the pollution problem.
There are two ways by which this pollution problem can be dwelt with. The first relates to the treatment of wastes to decrease their pollution. This involves the processing of solid wastes before disposal and the treatment of liquid wastes to permit the re-use of the water or reduce pollution upon final disposal.
A second approach is to develop an economic use for all or a part of the wastes. Liquid wastes from sewage disposal plants are used in some areas for watering agricultural land. Liquid wastes from other processing plants may also be used as a new source of water. Many industries are currently changing former waste products into marketable byproducts (副产品). Other industries are exploring potential economic uses for their waste products.

It can be concluded that ______.

A. byproducts from wastes lead to a prosperous market

B. countries of the world work together on water problems

C. some industries are now making economic use of wastes

D. great progress has been made in increasing water supply

正确答案是C