第 1 页精品文档---下载后可任意编辑托福考试阅读冲刺 为了让大家更好的预备托福考试，我给大家整理了托福考试阅读冲刺,下面我就和大家共享，来观赏一下吧。 托福考试阅读冲刺 1 It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species. The fossil record reveals that extinction has occurred throughout 第 2 页精品文档---下载后可任意编辑the history of Earth. Recent analyses have also revealed that on some occasions many species became extinct at the same time — a mass extinction. One of the best-known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when approximately 95 percent of all species died, mass extinctions can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the oceans. Such a change would probably lead to a mass ext...
