Everyone wants to reduce (17). But the pollution problem is as complicated as it is (18). It is complicated because (19) pollution is caused by things that benefit people. For example, exhaust from automobile caused large percentage (20) air pollution. But the automobile provides transportation to millions of people. (21) discharge much of the material that pollutes air and water, but factories give employment to a large number of people. Thus, to end or greatly reduce pollutions (22), people would have to stop using many things (23) benefit them. Most people do not want to do that, of course. But pollution can be gradually reduces in several ways. Scientists and engineers can work to find ways to lessen the amount of pollution that such things as automobiles and factories cause. Government can pass and enforce laws that require businesses (24) individuals to stop, or cut down on certain polluting activities.