Reading Comprehension
When discussing the causes of animal endangerment, it is important to understand that individual species are not the only factors involved in this difficult situation．Endangerment is a broad 1 , one that involves the habitats(栖息地)and environments where species live and interact with one another．Although some measures are being 2 to help specific cases of endangerment, the universal problem cannot be solved until the 3 environments where endangered species live are 4 by humans．There are many reasons why a particular species may become endangered, but habitat destruction is on top．
Our planet is continually changing, causing habitats to be changed and modified．Natural changes tend to occur at a gradual pace, usually causing only a slight 5 on individual species．However, when changes occur at a fast pace, there is little or no time for individual species to 6 and adapt to new circumstances．This can create disastrous results, and for this reason, rapid habitat loss is the 7 cause of species endangerment．The strongest forces in rapid habitat loss are human beings．Nearly every region of the earth has been affected by human 8 , particularly during this past century．The loss of microbes(微生物)in soils that formerly supported tropical forests, the 9 of fish and various aquatic(水族的)species in polluted habitats, and changes in global climate brought about by the 10 greenhouse gases are all results of human activities．
It can be 11 for an individual to recognize the effects that humans have had on specific species．It is also hard to identify or predict human effects on individual species and habitats, especially during a human lifetime． 12 it is quite obvious that human activities have greatly contributed to species endangerment． 13 , although tropical forests may look as though they are thick and healthy, they are actually highly susceptible(易受影响的)to destruction only because of the soils in which they grow 14 nutrients(营养)．It may take centuries to re-grow a forest that was cut down by humans or destroyed by fire, and many of the world’s severely threatened animals and plants live in these forests．If the present rate of forest 15 continues, huge quantities of plant and animal species will disappear．
