The human …….. (16) is only one small species in the living world. Many ……. (17) species exist on this planet. However, human beings have great influence on the rest of the world. ………..(18) are changing the environment by building cities and villages where forests once stood. They are …………(19) the water supply by using water for industry and agriculture. They are changing weather conditions by cutting down trees in the forests, and they are destroying the air by adding ……….. (20) to it. 16: A. kind B. race C. beings D. species 17: A. other B. these C. some D. others 18: A. Species B. They C. Human D. Their 19: A. polluting B. effecting C. changing D. affecting 20: A. polluted B. pollutants C. pollute D. pollution