题型：概要写作 题类：常考题 难易度：困难
人教版（新课程标准）高中英语必修五Unit 2 The United Kingdom单元测试
It is natural for species of animals to become extinct over millions of years. But over the past 200 years, humans have caused the process to speed up. In recent years, the total number of threatened animal species has increased from 5205 to 5345. In most cases this is a result of human activity. How are people speeding up the process of animal extinction?
First of all, people threaten the survival of animal species by destroying their habitats. As the human population grows, people keep building houses and factories in fields and woods. As they spread over the land, they destroy animals' homes. If the animals can't find a place to live, they die out. Sixteen kinds of Hawaiian birds have become extinct for this reason.
Overhunting is another way that humans are causing some animals to become extinct. In some parts of the world, the parts of rare animals are worth a lot of money. For example, some people will pay more than $3,000 for a single rhino horn. This encourages hunters to kill rhinos even though the animal faces extinction.
Humans are also polluting the air, water and soil. The effect of pollution on animal species can be complicated. For example, when waste from factories is dumped into rivers, the rivers become polluted. The fish that live in the rivers are poisoned, and the birds cannot lay strong eggs. And some, such as brown pelicans, have become rare and may die out.
Finally, when humans introduce new species into certain environments, the animals that already live there become threatened and face extinction. For example, when European settlers brought rabbits and foxes to Australia, they killed off many native Australian animals, including the bandicoots. Eventually, the rabbits took over the bandicoot habitats. Now bandicoots are threatened with extinction in their own land.
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