Pollution control is management of waste materials in order to minimize the effects of pol

lutants on people and the environment. The quality of human health and of the natural environment depends on adequate pollution control. In the United States much has been done to control the more noticeable pollutants since 1965: more subtle yet still hazardous pollutants, however, remain to be adequately controlled.

Four general approaches to pollution control are: the intermittent reduction of industrial activities during periods of high air-pollution conditions; wider dispersion of pollutants using such devices as taller smokestacks; reduction of pollutants in industrial emission; and change of an industrial process or activity in order to produce less pollution. Taller smokestacks may reduce the concentrations to which local people are exposed, but they are ineffective in reducing overall pollution.

Pollutants removed from waste flows to reduce emissions to air and water may be disposed of by burial or storage on land, practices that pose potential hazards. Recent legislation requiring extensive emissions reductions has resulted in large investments in pollution-treatment technologies.

The fourth approach — changing a manufacturing process or activity in order to produce less pollution — may involve either the production of fewer residuals, by means of an improved process, or the separation and reuse of materials from the waste stream. This method of pollution control is the most effective and, as the costs of pollution control and waste disposal increase, is considered one of the most efficient.

Pollution-treatment systems have been effective in reducing the massive quantities of water and air pollutants that have clogged and choked urban areas. Although the improvements have been significant, recent pollution-control legislation aims to go further in order to control the less visible but often hazardous chemical and gaseous pollutants that still contaminate many waterways and urban atmospheres.

The costs of pollution control — resulting from capital, maintenance, and labor costs, as well as from the cost of additional residuals disposal — generally go up rapidly as a greater percentage of residuals is removed from the waste stream. Damage from pollution, on the other hand, goes down as a greater amount of contaminant is removed. Theoretically, the level of treatment should correspond to a point at which total costs of treatment and of damage to the environment are minimized or the benefits of further treatment are proportionally much smaller than the increased cost. In reality, costs or damages resulting from pollution can rarely be assessed in terms of dollars.

According to the passage. All of the following can be objectives of pollution control EXCEPT______.

A．reducing polluting substances

B．controlling all the pollutants

C．restricting industrial activities

D．improving the environment and human health