这个段落的论述的中心是大学以传授知识本身为目的，作者使用了"通才教育"这个在西方国家非常流行的教育方式为佐证，在给出"通才教育"定义的本身，又用定语从句补充到了和题目第2个论点间的关系，从而进行了有力的对比，深化了段落中心。
2. Education
When people leave school，they wish they could breathe a sign of relief and leave learning behind. However，learning should last a lifetime. You exercise your body to stay strong，and you should exercise your mind to stay sharp. ……
在这个关于教育的话题中，作者在论述时用终身教育的好处来诠释教育的长期性和必要性，从而为下文的扩展作了很好的铺垫和过渡。【这个例子中的下定义的例子很"隐晦"】
3. School should teach children academic subjects which will be beneficial to their future careers. Therefore，other subjects such as music and sports are not important. To what extent do you agree or disagree with this opinion?(08年5月22日A类考题)
Academic subjects，such as reading and writing，play a vital role in the education system. Apart from activating creativity and imagination，it helps students lay a solid foundation of knowledge. Some might say that academic subject is to a student as a rifle is to a soldier，without which he is unable to fulfill his mission……【这句话还是非常非常精彩的。用了修辞比喻，句型也很好】
在这个主体段中，作者在开头便举出了一些学术课程的具体内容，从而给读者一个概念，同时也展现了作者对题目的解读能力。接下来我们再来看一个相似的用法：
4. Why have not alternative energies already replaced fossil fuels?
There are also problems with production stability. The amount of energy we need varies throughout the day，and conventional energy production，such as coal and oil，can be increased or decreased based on these variations. Alternatives like wind and solar power are limited because they can only produce electricity when it is sunny or the wind is blowing.
在这篇分析型大作文里，作者通过对化石燃料和可替代燃料的对比，突出了前者的优点，也揭示了后者的不足。通过将一个名词范围中的具体例子举出，是下定义的另外一种诠释。
综上所述，下定义可用于议论文的开头或者主体段里，但是它一般不适用于用在结尾段中。除了字典上的定义外，建议考生还可以从这个名词或短语的功能、目的、包含的具体例子等方面赋予它含义，这些方式都属于下定义。
【解析】下定义的确是广泛引用在雅思高分写作中的一种技巧。希望大家用心体会。