说明文：在四级作文中，实际上细化为原因类作文，最明显的原因类作文，如My Favorite Programme, My Ideal Job, The Career I Pursue,再就是Why I T ake the College English Test Band 6。
模板一：
Why Are There so Many Rural Laborers in Big Cities?
1.近来来越来越多的民工涌入大城市。
2.产生这一社会现象的原因。
For a number of years, there has been a steady rise in the number of rural laborers who flood into big cities. Many men work on construction sites, while many women work as dishwashers in restaurants or babysitters for city dwellers. Three reasons, in my mind, can account for this social phenomenon.
First and Foremost,the limited land can no longer produce enough crops for an ever-increasing rural population.In the second place,there are far more opportunities in big cities----rural laborers dream of earning money through hard st but by no means the least, many of them want to live permanently in big cities, because they admire the way of living there, and wish their children to receive good education.
I firmly believe that if we try our best to create a healthy social atmosphere, rural laborers will make greater contribution to our nation.
结构点评
这篇作文谈论的是一种社会现象。第一段分三句，首句引入大量农民工进入大城市这一现象，第二句举例子进行说明，第三句是个过渡，引起解释原因的段落。第二段分三个方面来解释原因。第三段是乘法的结束语。这是我们大家熟悉的结构。
妙笔生花
第一段首句是个经典句型，大家应熟记。第二句是举例说明，construction site 表示“建筑工地”，babysitter表示“帮人看孩子的人”。第三句使用了插入语，强调了句子主语。
第二段分三个方面来解释这一社会现象。第一点中no longer 和ever-increasing的使用突显了矛盾，其中rural指“乡村的”。第二点中的far more 亦可用much more，后使用破折号，引出进一步的说明。第三点中permanently 和admire 分别指“永久地”和“羡慕”，接受教育是“receive education”。
第三段非常简洁，是宾语从句嵌套条件状语从句的情形。条件状语从句的语气平和舒缓，显得非常客观。
模板二：
还有些题目也是原因类题型，像It Pays to Be Honest, Harmfulness of Fake Commodities, Don’t Hesitate to Say “NO”. 这些都是从写现象-----原因------后果的三段论式。
今天我们练习写，主题句已经给出：It Pays to Be Honest
1当前社会上存在许多不诚实的现象
2诚实利人利己，做人应该诚实
Nowadays, every one of us has been confronted with too many instances of dishonesty either through the mass media or in daily life………….We can’t help asking ourselves: What is wrong with our society? Is honesty going out of style?
Honest should and would never go out of style. For any individual, honesty ……
All that has been discussed above points out an undeniable fact that it pays to be honest. Honesty ……..
模板三
Video Games
The recent years have witnessed表明，目击an unfavorable social phenomenon—more and more college students become indulged 迷恋in video games. Some of them play video games overnight, which will inevitably hinder妨碍their study. Others even play truant逃避to enjoy themselves.
After contemplating沉思and meditation沉思, we can find three possible reasons to account for this trend. First of all, the information technology is developing at a fantastic speed and video games become more and more advanced and attractive. What’s more,many students lack self-control to such an extent that they play for long hours even if
