参考：In modern society, environment related issues have confronted ecological scientists, government agencies and the general public. (引自雅思高分范文p16)

3). 定义法。即通过对话题词的定义的介绍，这种方法有一定难度，考生需要有渊博的知识，才能做到对名词的解释，但对特别明显的词语，考生可借鉴这种方法。

请看一例：

The main purpose of public libraries is to provide books and they should not waste their limited resources and space on providing expensive hi-tech media such as computer software, videos and DVDs. To what extent do you agree or disagree with this statement?

本题中的话题词为图书馆，可以解释的词也是图书馆比较方便容易。那么到底如何解释呢，比如说图书馆在传统意义上来看，是收藏书的地方，而现在因为科技发展，使得图书馆的意义发生改变，从而引出话题。这里同样可以用形式主语：

It is generally believed that public libraries are places with a large collection of books; however, the digital time has given it a new means of storing and retrieving information.

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