之所以有这样的讨论，重要原因在于，很多同学认为文章中的每个段落、每个句子甚至每个单词对于阅读理解而言都同等重要。是不是这样呢?我们一起来看一个雅思考试中所出现的段落。
Privately held companies are voluntarily adding more scrutiny, as well. In a recent survey that drew responses from 1400 CFOs in such businesses, 58 percent said they are responding to new corporate-governance standards. Of those, 36 percent are creating or expanding internal auditing, according to Robert HALF management Resources. An American company with $3 billion to $4 billion in revenue typically has about 16 internal auditors. The job is often a training ground for future management positions, but those who stay in the field and become directors earn an average of just under $100,000. The IIA offers certification for internal auditors, but many firms do not require it.
参考译文：
私营公司现在也开始更加注重企业的内部审计工作。调查结果显示，一项对1400位公司首席财务执行官的调查结果显示，有58%的企业正在采取措施以符合系的公司管理标准的要求。当然，根据罗伯特哈夫管理资源公司(Robert HALF management Resources )的说法，36%的公司正在建立或是加大内部审计工作的力度。一般来说，营业额在30亿到40亿美元的一个美国公司就会有16个内部审计员。这种职位通常都是晋升为管理阶层的一个过渡，但是从事此项工作并最终成为主管的人员年薪都可达到100,000美元左右。IIA负责颁发内部审计员资格证书，但很多公司其实并不需要这种认证。
这段话的每一句的含义，我们现在都了解了。很明显，这段话最大的特点是几乎每句话都出现了具体的数字。那么作者写这段话的目的是什么呢，是要强调这些数字的重要性吗?显然不是。这些数字本身并没有什么实际意义。提出这些数字的目的，只是为了体现出“私营公司现在也开始更加注重企业的内部审计工作”。大家可以体会一下是不是这样。
显然，第一句话是全段的核心，其他句子都是从某一个侧面支持或论证这句话的。
我们来梳理一下阅读这段话给我们的启示。
段落由两个部分组成，即重要的内容，和次要的内容。
我们以后可以把重要的内容叫做主题，而次要的内容叫做支持性的细节。因为雅思考试阅读部分的文章都是论说文，即以说理为主，说明为辅。
我们先来看一下主题句的特点：
内容：一般比较抽象概括
位置：一般出现在两个位置的可能性最大：每段话的开头和结尾。
通常而言，主题句就是一段话的第一句。后面的句子一般为支持性的细节，以解释、发展或是支持主题句所表现的主要论点。
The recent string of corporate scandals provided a rude awakening to the importance of these internal checks. In the case of WorldCom, it was internal auditor Cynthia Cooper who blew the whistle on the company for inflating profits by $3.8 billion. She didn’t intend to be a hero, she said to Time magazine when it named her one of its Persons of the Year. She was just doing her job.
Chief constables had disapproved of the use of league tables. They complained that they provoked unfair criticism because they did not compare like with like. Mr. Denham said the graphs were easier to comprehend than tables. “As people get familiar” with this type of graphical presentation they will realize it contains a lot of data that can be understood after an initial glance. “ The spidergrams are based on five indicators: reducing crime, investigation crime, public safety, deployment of resources and the view of a focus group of local citizens.
有时候主题句也会出现在整段话的最后。这样的结构安排，通常出现在一个讨论困难的、不为大众所接受的话题或者文章的主要目的是为了说服读者接受某种结论的段落中。因为先把道理说清楚，那么读者就会比较容易接受新的观点和看法。
If the wind becomes gusty after a period of calm, you should seek shelter. The sky needs careful watching too. Gradual darkening and “boiling” clouds should quicken your pace. Lightening and thunder are common enough storm indicators, but few people realize that the brightness of the lightening is not nearly as important as the number of lightning flashes. The signs of an oncoming storm are many, and a person’s life may depend on his ability to interpret them,
主题句也可能在段落当中：
From one perspective, this huge customer base represents a hair-raising social liability. Surgical and hospital costs fro regular heart transplants run as high as $500,000. these procedures haven’t burdened the medical system so far – but only because the supply of transplantable hearts has been limited to about 2000 a year. Abiomed plans to price its heart between $75000 and $10000 initially, and with volume production, the price could fall as low as $10000. However, even at the lower price, artificial hearts are an issue that will lead into moral quicksands, says medical ethicist David Steinberg of the Lahey Clinic in Burlington, Mass. What happens, Steinberg muses, “if heart replacement – and intervention directly and visibly linked to who will live and who will die—becomes available only to those who can afford it?
