2013年大学英语四级写作题型及范文：说明文

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　　说明文是以说明为主要表达方式用来说明事物，阐明事理的一种文体。它通过揭示概念来说明事物的特征、本质及其规律性，给人准确的科学知识或正确思想。一般可分为实体事物说明和抽象事物说明两大类，词典、教材、论文、实验报告、产品说明书、广告、解说词及科学小品等都属于说明文。
　　按写作方法,英语说明文主要分为下面六种类型:
　　1.例证法
　　这是用具体例子来说明人或事物的特征、本质及其规律的方法,所用例子必须有代表性、典型性,能体现人或事物的本质特征。这是用特殊来说明一般的方法。通常在主题句后,用 For example 或 For instance 等短语引导出具体的例子。例如:
　　Our life today depends very much on energy. For example, machines have made our life easier than it used to be. The machines use energy, and energy is needed for heating, lighting, communications, carrying goods-everything. Factories use a great deal of energy to make the things that we use and buy and sell.
　　这段主要是讲能源问题。第一句为主题句,概括地说出"我们目前的生活很大程度上依赖能源"。接着用举例的方法从三方面说明能源的作用。
　　2.定义法
　　下定义就是给说明对象一个明确概念。这是科学而严密的说明方法。它既能揭示事物的本质特征,勾勒其大概,描绘其轮廓,同时也能确定事物的范围和界限。下定义是多方面的,可以给人、事物、思想等下定义。例如:
　　An ideal teacher must have the following characteristics. He should know his subject, but he can make mistakes if he is willing to learn. His personality is as important as his scholarship. An ideal teacher must be enthusiastic. He should be a bit of an actor and he shouldn't be afraid to show his feelings and express his likes and dislikes. An ideal teacher is one who grows, learns, and improves himself along with his students.
　　本段的展开是通过对"一个模范教师"下定义的方法,关键词"ideal teacher"在文中多次重复,能加深读者的印象。
　　3.分类法
　　分类法是对同属不同类或同类而不同种的人或事物,根据不同性质进行分门别类地说明的方法。分类是人类认识客观世界的重要手段之一。分类必须遵守分类规则,使分类对象具有统一属性,依据同一分类标准,并使分类的子项相互排斥,不互相包蕴。例如:
　　As far as political views are concerned, people fall into three categories. First are the conservative people. Conservatives are opposed to sudden or great changes. Second are the liberal people. These people are in favor of progress and reform. But their opinions often seem too idealistic. Third are the moderate people. The moderates keep everything within reasonable limits. They are more practical in this hard world. In my opinion, most people seem to belong to this group.
　　本段把人按政治观点分为三类:保守派(conservative people)、自由派(liberal people)和温和派(moderate people),并对他们各自的特征进行了简要的分析。
　　4.因果关系法
　　事物变化的原因和结果是紧密相关的。如果某个现象的存在必然引起另一个现象的发生,那么,这两个现象之间就具有因果关系。因果关系包括"由果推因"(由结果去推测原因)和"由因推果"(由原因去推测结果)两种情况。因果关系符合人们的日常思维逻辑,因而在写作中得到广泛应用,常用 because, as, since, so, now that, if...then, the reason is that...等表示因果关系。例如:
　　Of the four seasons, I like spring best. I prefer spring because it is a season of much joy and gaiety. New life bursts out everywhere. Plants wear a green coagain and colorful flowers blossom in gardens and mountains. The old come outdoors for fresh air and the young plan for outdoor activities. Life becomes so energetic and happy.
　　第一句为本段主题句,末句是总结句。在主题句后, 作者用了四个句子阐述自己喜欢春天的理由。
　　5.比较对照法
　　有意识地把两种相反、相对的事物或同一事物相反、相对的两个方面放在一起,用比较的方法加以描述或说明,指出其相同点,这种写法叫做"比较";指出其不同点,叫做"对照"。比较和对照各有不同的侧重,但两种方法经常结合使用。
　　进行比较对照通常有两种方式。第一种方式采用"先A后B"的结构,即A1,A2,A3...; B1, B2, B3...。第二种方式采用"AB交错"结构,即A1,B1;A2,B2;A3,B3...。第一种方式采用先A后B的结构实际上是把一个段落(或一篇文章)分割为两部分,先全面讲A,再全面讲B,这样做较难收到强烈的对比效果。多数人认为第二种方式比较好,因为把对比的双方AB逐点交错,可以避免行文的单调沉闷,对比的效果也会更鲜明突出。例如:
　　It is easy to be a winner. A winner can show his joy publicly. He can laugh and sing and dance and celebrate his victory. People love to be with winners. Winners are never lonely. Unlike winners, losers are the lonely ones of the world. It is difficult to face defeat with dignity. Losers can not show their disappointments publicly. They can not cry or grieve about their defeat. They may suffer privately, but they must be composed in public. They have nothing to celebrate and no one to share their sadness.
　　这段采用先A后B的对照方式,阐述胜利者和失败者的不同特征。这种写法较易操作,但行文往往比较平淡单调。再来看看AB交错的比较方式:
　　I like having a twin sister. When she’s happy, I’m happy. When she feels unhappy, I feel the same. Often, I know what she’s going to say. Sometimes, I know what she’s thinking. I like what she likes. I hate what she hates. We like the same music, the same food and the same books.
　　这段采用AB交错的比较方式,阐述孪生姐妹的相同特征。这种写法较流畅自然,给读者的印象也更鲜明突出。