This system usually gives the required environmental benefit at the least cost. The limits it imposes on pollutant emissions are no more stringent or costly than is necessary to achieve the conservation goal.

• 这个制度通常以最低成本，便能提供所需的环境效益，因为制度对污染排放物的限制，是为达至保护目标的最低要求，并非特别严格或昂贵。