Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the word that best fits each of the numbered blanks.

Everyone wants to reduce pollution, but the pollution problem is as complicated as it is serious. It is complicated because (29) __________ pollution is caused by things that benefit people. For example, exhaust from automobiles causes a large percentage of all air pollution, (30) __________ the automobiles provide transportation for millions of people. Factories discharge much of the material that pollutes air and water, but factories give employment to a large number of people.

Thus, to (31) __________ or greatly reduce pollution immediately, people have to stop using many things that benefit them. Most of the people do not want to do that, of course, but pollution can be gradually reduced in several ways. Scientists and engineers can work to find ways to lessen the amount of pollution (32) __________ such things as automobiles and factories cause. Governments can pass the laws that require businesses and individuals to stop, or cut down on certain polluting activities.

It is complicated because (29) __________ pollution is caused by things that benefit people