段落的构成(Paragraph Structure)段落是由表达单一中心思想(controlling idea or central idea)的一组句 子(包括主题句topic sentence,扩展句supporting sentences及结论句 concluding sentence)构成，是文章结构的基本独立单位。一、主题句主题句(topic sentence)是表达段落主题的句子。它用以概括段落大意， 要求全段其他文字都围绕它扩展。例：My mother has passed along to me certain rules for getting along with others. Dont argue withparents;they will think you dont love them. Dont argue with children; they will think themselves victimized.Dont argue with spouses; they will think you are a tiresome mate. Dont argue with strangers; they will think you are not friendly. My mothers rules, in fact,can be summed up in two words: Dont argue.主题句中提出的certain rules”指的是什么？扩展句中通过四个“Don，t argue”逐一加以交代。从结构来看，这是一个比较典型的段落，它包 括了主题句，扩展句和结论句。1. 主题句的位置过外表、行动或变化用语言描绘一个人，一个物体，一个地方或一个 场面。(1)示范段落分析例：Tsunami is Japanese for harbor wave.It is, in fact, a series of waves which travel outward on the ocean surface in all directions in a kind of ripple effect. Since the waves can start out hundreds of miles long and only a few feet high, they would not necessarily be noticeable to a passing ship or a plane flying overhead. As the waves get closer to shore, they decrease in speed and increase in height. They approach the coastline as a series of high and low water levels, approximately10-45 minutes apart,with their speed decreasing to about 30-40 mi/hr (50-60 km/ht).The depth of the water and the layout of the coastal area can affect the tsunamis configuration when it hits the shore. It can grow to 30-50 meters high and smash into the shore as a wall of water or sweep over the land as a fast-moving flood. Although tsunamis can happen in any large body of water, most occur in the Pacific Ocean.主题句: A tsunami is a series of waves.细节 1: extension宣田节 2: speed(statistics used)细节 3: height(statistics used) 在上面段落中，作者用细节(包括数据)描述了海啸的宽度(extension)、 速度(speed)和高度(height),从而告诉读者海啸是什么样子。例：The kitchen was in a mess. Along the left wall werethe counter and sink covered with dirty dishes and garbage. On the far wall the washing machine groaned under a load of filthy clothes. Right next to the door where I was standing, on my right,! saw a table cluttered with old newspapers, an overturned catsup bottle, and a wet, half-eaten hot dog.At the far end of the right wall the refrigerator stood with the door open, ajar of milk dripping down from the top shelf.lt was the messiest kitchen I had ever seen.主题句：The kitchen was in a mess.细节 1: Along the left wallounter and sink仑田节 2: On the far wallwashing machine细节 3:Right next to the door, on my righttable细节 4: At the far end of the right wall一refrigerator结论句:It was the messiest kitchen I had ever seen.(2)使用描述法扩展段落的建议1主题句给读者一个深刻的印象写一段好的描述段落要注意两个方面：首先给读者一个深刻的印象， 然后运用充分的细节。这种深刻的印象必须首先吸引读者，因此不要 在主题句中用太琐碎的东西冲淡这一印象。比较下面两个主题句：a. The kitchen is in a mess.b. The kitchen is a place where the hostess does almost all the housework and as a consequence it is not always attractive and neat.显然，前一句主题句比后一句更吸引读者，因为它能给人以更深刻的 印象。 提供充足的细节具体和生动的细节是成功的描述所不可缺少的。在海啸一例中，作者 通过海啸外表的生动细节以及速度和高度的具体数据描述海啸。在厨 房一例中，主题句后，作者提供细节来描绘厨房是怎样的乱七八糟。 记住不要提供无用的细节使读者失望。 使用空间顺序法组织段落好的描述还在于把一大堆具体的细节按空间顺序组成一个整体。在海 啸一例中，作者按照从表面到海底，从远到近的顺序描绘。在厨房一 例中，作者按照从左到右，从近到远的顺序描绘。 使用有新意的明喻和暗喻 明喻(Similes)和暗喻(metaphors) nJ使描述更加生动。但要尽量避免使 用己经用得太滥的比喻。2. 定义法定义法(definition)就是解释某事物是什么，不是什么。写下定义段落 时，通常把概念或要下定义的事物置于一个大的类别中，然后解释该 事物与同一类别的其他事物有何不同。下定义法多用作推展段落的辅 助方法。在科普文章的写作中，定义法是必不可少的。通过下定义， 可以使读者对该事物有一个更直接的认识。常出现在定义法中的词语 有:refer to,mean, call 等。(1)示范段落分析例：Automation refers to the introduction of electronic control and automation operation of productive machinery. It reduces the human factors, mental and physical, in production, and is designed to make possible the manufacture of more goods with fewer workers. The development of automation in American industry has been called the “Second Industrial Revolution.本段文字使我们了解了 “automation”和“Second Industrial Revolution,两个概念，分另U 由“refers to和“been called, 引出。例:Pencil is a pointed implement used in writing or drawing to apply graphite or a similar colored solid to any surface, especially paper. From prehistoric times lumps of colored earth or chalk were used as markers. The Egyptians ruled lines with metallic lead, as did medieval monks. The so-called lead pencil-a rod of graphite encased in wood-came into use in the 16山 cent.From the late 18th century,pulverized graphite was mixed with clay to bind it and to provide different degrees of hardness-the more clay, the harder the pencil.Today the mixture is forced through dies, cut to the required length,and kiln-fired. The rods are laid in grooves of a thin board, a similar board is placed over them, and the wood is shaped into pencils, usually of round or hexagonal cross section. Pencils are also manufactured with cores of colored pigments mixed with clay and wax and of other materials.Mechanical pencils are commonly made of metal or plastic, the cores (or leads) being advanced by operating a screw