TPO (TOEFL Practice Online) 是美国教育考试服务中心(Educational Testing Service，简称ETS)专为参加托福TPO33口语Task4答题技巧及模版：
Carrying Capacity
An animal species needs to have enough resources, like food and water, to survive in any given environment. However, because resources are limited, only a certain number of animals of a particular species are able to survive in a given habitat. The greatest number a habitat can support is known as the carrying capacity. If nothing happens to disrupt or unbalance the relationship between the animal and its habitat, the carrying capacity will remain stable. However, a carrying capacity is not fixed. If there is a significant disruption, such as an environmental event that alters the amount of available resources in the habitat, the carrying capacity will change.
Explain the concept of carrying capacity using the example of the moth and Ragwort.
1、题目关键词：explain the example, the concept
2、答题要领：
(1)briefly state the main idea of the reading passage
(2)concentrating on the idea given by the professor. When orally summarizing the lecture, test takers are supposed to include the main points and some examples as well.
3、阅读材料要点：
(1) The greatest number a habitat can support is known as the carrying capacity.
(2) If nothing happens to disrupt or unbalance the relationship between the animal and its habitat, the carrying capacity will remain stable. However, if there is a significant disruption, the carrying capacity will change.
4、听力材料要点：
(1) The professor gives an example of a species of moth that lives in Europe.
(2) The moths lived in the field for many years because there were plenty of Ragwort plants of them to eat. So the number was stable.
(3) However, for one year, it rained a lot less, so the Ragwort did not grow as well. So that year, the moth population was a lot smaller.
(4) The next year, it rained more. Thus, the Ragwort plants grew a lot more. And the population of moth returned it that it was before.
5、模板：
(1) In this set of materials, the reading passage is (the title of the reading passage) and the listening material is a lecture by a professor on the same topic. 当然，如果你觉得你的听力材料的理解率很高也不用谈及阅读材料中的内容。只是第一段说起来实在太easy了。
(2) In the reading passage, it introduces a concept called…
(3) In the lecture, the professor… 不但要包括观点而且要包括教授所给的例子。
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