Choose the suitable word to fill in each plank.

Everyone wants to reduce pollution. But pollution problem is (21)………complicated as it isserious. It is complicated (22) ………much pollution is caused by things that benefit people. For example, exhaust (23) …….. automobiles causes a large percentage of all air pollution. But automobiles (24)……. transportation for millions of people. Factories discharge much of the material (25) …………. pollutes the air and water, but factories give employment to a large (26) ……. of people. Too much fertilizer or pesticide can run soil, but fertilizer or pesticide (27) …… important aids to the growing of crops. Thus, to end (28) …OR/ AND…greatly reduce pollution immediately, people would have to (29) ……using many things that benefit them. Most people do not want to do that, of course. But pollution can (30)

……gradually reduced in several ways.

Everyone wants to reduce pollution. But pollution problem is (21)………complicated as it isserious.