[填空题]

Pollution is a "dirty" word. To pollute means to contaminate--to spoil something by introducing impurities which make {{U}} (31) {{/U}} unfit or unclean to use. Pollution comes in many forms. We see it, smell it, {{U}} (32) {{/U}} it, drink it, and stumble through it. We literally lived in and breathe pollution, and {{U}} (33) {{/U}} surprisingly, it is beginning to {{U}} (34) {{/U}} our health, our happiness, and our very civilization.
Once we thought of pollution {{U}} (35) {{/U}} meaning simply smog--the choking, stinging, dirty {{U}} (36) {{/U}} that hovers over cities. But air pollution, while it is {{U}} (37) {{/U}} the most dangerous, is only one type of contamination among several {{U}} (38) {{/U}} attack the most basic life functions.
Through the uncontrolled use of insecticides, man has polluted the land, {{U}} (39) {{/U}} the wildlife. By {{U}} (40) {{/U}} sewage and chemicals into river and lakes, we have contami