Fill in the blank with the most suitable word

VI. Fill in the blank with the most suitable word.

Everyone wants to reduce pollution. But pollution problem is……………. (1) complicated as it is serious. It is complicated     ………………. (2) much pollution is caused by things that benefit people. For example, exhaust………………. (3) automobiles causes a large percentage of all air pollution. But automobiles ……………… (4) transportation for millions of people. Factories discharge much of the material ………………(5) pollutes the air and water, but factories give employment to a large ……………….  (6) of people. Too much fertilizer or pesticide can ruin soil, but fertilizers and pesticide ………………. (7) important aids to the growing of crops. Thus, to end……………… (8) greatly reduces pollution immediately, people would have to ………………… (9) using many things that benefit them. Most people do not want to do that, of course. But pollution can ………………. (10) gradually reduced in several ways.