(一)篇章定义
与主题有关的篇章定义，理解它有助于做主旨题。
例1 Oceanography has been defined as "The application of all sciences to the study of the sea".
Before the nineteenth century, scientists with an interest in the sea were few and far between. Certainly Newton considered some theoretical aspects of it in his writ-ings, but he was reluctant(不愿意)to go to sea to further his work.
For most people the sea was remote, and with the exception of early interconti- nental travellers or others who earned a living from the sea, there was little reason to ask many questions about it, let alone to ask what lay beneath the surface. The first time that the question "What is at the bottom of the oceans?" had to be answered with any commercial consequence was when the laying of a telegraph cable from Europe to America was proposed. The engineers had to know the depth profile(起伏形状)of the route to estimate the length of cable that had to be manufactured.
It was to Maury of the US Navy that the Atlantic Telegraph Company turned, in 1853, for information on this matter. In the 1840s, Maury had been responsible for encouraging voyages during which soundings(测深)were taken to investigate the depths of the North Atlantic and Pacific Oceans. Later, some of his findings aroused much popular interest in his book The Physical Geography of the Sea .
The cable was laid, but not until 1866 was the connection made permanent and re- liable. At the early attempts, the cable failed and when it was taken out for repairs it was found to be covered in living growths, a fact which defied contemporary scientific opinion that there was no life in the deeper parts of the sea. Within a few years ocea- nography was under way. In 1872 Thomson led a scientific expedition(考察), which lasted for four years and brought home thousands of samples from the sea. Their clas- sification and analysis occupied scientists for years and led to a five-volume report, the last volume being published in 1895.
上述文章第一段就是一个定义：Oceanography has been defined as "The application of all sciences to the study of the sea."(海洋学是综合应用所有科学对海洋进行的研究)。这肯定与主题有关，于是看到下题。
This passage is mainly about
A. the beginnings of oceanography
B. the laying of the first undersea cable
C. the investigation of ocean depths
D. the early intercontinental communications
可以直接确定A项为答案。B.C.D项均为原文中的细节，不能成为主旨题的答案。
(二)具体定义
就是对文中某个现象或术语加以定义。这种具体定义有时成为词义题的考试内容。
例2 Statuses are marvelous human inventions that enable us to get along with one an- other and to determine wher we "fit" in society. As we go about our everyday lives, we mentally attempt to place people in terms of their statuses. For example, we must judge whether the person in the library is a reader or a librarian, whether the tele- phone caller is a friend or a salesman, whether the unfamiliar person on our property is a thief or a meter reader, and so on.
The statuses we assume often vary with the people we encounter, and change throughout life. Most of us can, at very high speed, assume the statuses that Various situations require. Much of social interaction consists of identifying and selecing among appropriate statuses and allowing other people to assume their statuses in rela- tion to us. This means that we fit our actions to those of other people based on a con- stant mental process of appraisal and interpretation. Although some of us find the task more difficult than others, most of us perform it rather effortlessly.
A status has been compared to ready-made clothes. Within certain limits, the buyer can choose style and fabric. But an American is not free to choose the costume(服装)of a Chinese peasant or that of a Hindu prince. We must choose from among the clothing presented by our society. Furthermore, our choice is limited to a size that will fit, as well as by our pocketbook(钱包). Having made a choice within these lim- its we can have certain alterations made, but apart from minor adjustments, we tend to be limited to what the stores have on their racks. Statues too come ready made, and the range of choice among them is limited.
In the first paragraph, the writer tells us that statuses can help us
A. determine whether a person is fit for a certain job
B. behave appropriately in relation to other people
C. protect ourselves in unfamiliar situations
D. make friends with other people
这道题问statuses的作用，这是第一段的内容。第一段首句就是一个定义：Statuses are marvelous human inventions that enable US to get along with one another and to determine wher we "fit" in society.这个定义为第一段的主题句，也是本题的相关句，由此可知B项为正确答案：(statuses有助于)人们在人际交往中保持言谈举止得体。
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