7、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（棲息地）and environments where species live and interact with one another．Although some measures are being taken to help specific cases of endangerment, the universal problem cannot be solved until humans 2   the natural environments where endangered species live．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 altered and modified．Natural changes tend to occur at a   3   pace, usually causing only a slight  4   on individual species．However, when changes occur at a fast pace, there is little or no time for individual species to   5   and adjust to new circumstances．This can create disastrous results, and for this reason, rapid habitat loss is the primary cause of species endangerment． The strongest   6   in rapid habitat loss are human beings． Nearly every region of the earth has been affected by human activity, particularly during this past century．The loss of microbes（微生物）in soils that   7    supported tropical forests, the   8   of fish and various aquatic species in polluted habitats, and changes in global climate brought about by the   9   of greenhouse gases are all results of human activity．

It can be difficult for an individual to   10   the effects that humans have had on specific species．It is hard to identify or predict human effects on individual species and habitats, especially during a human lifetime．But it is quite   11   that human activity has greatly   12   to species endangerment．   13  , although tropical forests may look as though they are thick and healthy, they are   14   highly susceptible（易受影響的）to destruction．This is because the soils in which they grow   15   nutrients． 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 current rate of forest loss continues, huge quantities of plant and animal species will disappear．

1．A．theme                   B．project               C．issue                   D．experiment

2．A．worsen                 B．protect                C．construct            D．ignore

3．A．gradual                 B．single                 C．stable                  D．rapid

4．A．a(chǎn)nxiety                 B．improvement        C．impact             D．burden 

5．A．survive                 B．react                   C．reflect                 D．live

6．A．ruins                     B．objections            C．limitations            D．forces

7．A．formerly               B．formally              C．freely                  D．usually

8．A．a(chǎn)ppreciation           B．destruction          C．extinction            D．existence

9．A．escape                  B．leak                     C．release                D．relief

10．A．cause                  B．remind                C．remember            D．recognize

11．A．reasonable           B．a(chǎn)pparent              C．possible              D．natural

12．A．devoted               B．donated               C．contributed          D．a(chǎn)dapted

13．A．In short               B．By contrast          C．As a result           D．For example

14．A．naturally              B．a(chǎn)ctually               C．fully                    D．completely

15．A．lack                    B．contain                C．reduce                D．limit