英语专业四级考试听力复习材料： Population Growth

　　It is well-known that there has been a drastic increase in world population. But it is probably les well-known that the extinction rate of wildlife species is experiencing a parallel trend.
　　Take the United States for instance. In 1990, U.S. population reached an unprecedented level of 250 million, which is approximately 250 times of that of 1800. On the other hand, wildlife species are disappearing from the country at an alarming rate. By 1990, about 70 wildlife species would never be seen in U.S. We are fully justified in declaring that the explosive population growth has had an adverse effect on the survival of wildlife species and will be a constant threat to the wildlife resources if no immediate actions are taken.
　　Nothing has ever equaled the magnitude and speed with which the human species is altering the physical and chemical world. It has been demolishing the environment we are living in.