四六级考前阅读突破第一讲：抓住文章的主题

I. TOPIC OR SUBJECT

首先来看一看哪些问题是考察文章的主题的。

1. What is the main subject (topic) of the passage?
2. What is the passage about?
3. The passage is about ______.
4. What does the passage mainly discuss (illustrate, deal with)?
5. What is discussed (talked about) in the passage (paragraph)?
6. What is the general topic of the passage?
7. The passage centers on ______.

在这里我们要区分两个概念：话题和主题；主题和主体思想。
一篇文章可能有一个话题，也可能有多个话题，但只能有且只有一个主题，所以简单的说，主题是一篇文章中最主要的一个话题。由于有这个区别，所以就要求我们分清主次，抓住文章的主要话题。
此外，主题是文章的论题范围，而主题思想是观点意见或者结论性的看法。

下面我们来看一篇文章，找出这篇文章中有几个话题，哪一个是主题。

IA.
Although most universities in the United States are on a semester system, which offers classes in the fall and spring, some schools observe quarter system comprised of fall, winter, spring and summer quarters. The academic year, September to June, is divided into three quarters of eleven weeks each beginning in September, January, and March; the summer quarter, June to August, is composed of shorter sessions of varying length. Students may take advantage of the opportunity to study year around by enrolling in all four quarters. Most students begin their programs in the fall quarter, but they may enter at the beginning of any of the other quarter.

可以看出，这篇文章有两个话题semester system 和quarter system。哪一个是主题哪？不难看出，地一个话题只是作为比较对比，目的是引出第二个话题，所以第二个话题是主题。
 
再看一篇文章首先分析文的结构，可以看出该段落由两个部分组成-镁的提炼及方法、发展等和镁的用途。再来分析一下5个选项。发现5个选项文章中都提到过，都是文章的话题，但仔细分析，A，B是关于海水的用途和处理，只在第一句话中提到，C选项light weight是物理性质，不是化学性质，E选项从属于选项D，所以只有D是正确答案。

IB.
Magnesium is another mineral we now obtain by collecting huge volumes of ocean water and treating it with chemicals, although originally it was derived only from brines or from the treatment of such magnesium-containing rocks as dolomite of which whole mountain ranges are composed. In a cubic mile of seawater there are about four million tons of magnesium. Since the direct extraction method was developed about 1941. Production has increased enormously. It was magnesium from the sea that made possible the wartime growth of the aviation industry. For every airplane made in the United States (and in most other countries as well) contains about half a ton of magnesium metal. And it has innumerable uses in other industries where a lightweight metal is desired, besides its longstanding utility as an insulating material, and its use in printing inks, medicines, and toothpastes.

What is the main topic of this passage?
A. Uses of seawater
B. Treatment of seawater
C. Chemical properties of magnesium
D. Derivation and uses of magnesium
E. Aviation industry