由于一篇成人英語三級考試閱讀文章通常在250詞左右，一個定義可能占幾行，這時定義很可能作為考點。閱讀時只需圈出被定義的詞就行了。定義可以分為以下兩種。

　　(一)篇章定義

　　與主題有關(guān)的篇章定義，理解它有助于做主旨題。

　　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(起伏形狀)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(測深)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個定義：Oceanography has been defined as "The application of all sciences to the study of the sea."(海洋學(xué)是綜合應(yīng)用所有科學(xué)對海洋進(jìn)行的研究)。這肯定與主題有關(guān)，于是看到下題。

　　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

　　可以直接確定A項為答案。B.C.D項均為原文中的細(xì)節(jié)，不能成為主旨題的答案。