3．1关于写主题句的建议
1）要写合乎语法的句子
Example 1： Two causes of the American Civil War．
这个句子是个不完整的句子，不合乎语法，因此不能用作主题句。
Example 2： There were two causes that led to the American Civil War．
重写后的句子合乎语法，是个较好的主题句。
2）要使用限写词限定主题
为了正确表达观点，好的主题句经常使用关键词或词组，即限制词（controllers）限制这一观点。
Example 3： Air travel is more convenient than train for at least three reasons．
从上例主题句我们得知作者将要写"air travel"（ topic），他将要把 "train"（ aspect）和" air travel"作比较，并且陈述"reasons"。由此可见，作者在"aspect"（方面）和"reason"（原因）两方面限制他的主题。
3）要注意主题的可写性
所定的主题不能太笼统，也不能太具体。
Example 4： In Hemingway's story "Soldier's Home"，Krebs tells his mother that he wants no part of God's Kingdom．
这个句子太具体以至于无东西可写，无法展开段落。
Example 5： In Hemingway's story "Soldier's Home"， Kreb is a lonely， cynical veteran．
这个句子可作为主题句，因为可以围绕"lonely，cynical"展开段落。
Example 6： Let me tell you something about overpopulation．
这个句子太笼统，作为一个段落的主题太大，难于驾驭。
Example 7： Why has the world population been increasing sorapidly in the last decades？
这个句子是个较好的主题句，作者用"the reasons for overpopulation in the last decades"，从"原因"（cause）和"时间"（time）两方面限制了主题，能在一个段落内论述。
Exercise 3-1
Directions： Identify the areas which limit the topic sentences．
3．1．1 Soccer has become increasingly popular in the U． S． in the last ten years．
Topic：_____________
Limitations：________________________________________________
3．1．2 Pollution has caused three major problems in the last decades．
Topic：______________
Limitations：________________________________________________
3．1．3There are two kinds of memory： short-term and long-term．
Topic：____________
Limitations：________________________________________________
3．1．4 Women are playing an increasingly important part in society today．
Topic：____________
Limitations：________________________________________________
3．1．5 Women are paid less for equal work than men in some companies．
Topic：____________
Limitations：________________________________________________
Exercise 3-2
Directions： Write two topic sentences for each of the topics，limiting the topic in different ways．
3． 2． 1 Topic： the study of English
Topic Sentence 1：__________________________________________
Topic Sentence 2：___________________________________________
3．2．2 Topic： college students today
Topic Sentence 1：__________________________________________
Topic Sentence 2：__________________________________________
3．2．3 Topic： women in China
Topic Sentence 1：__________________________________________
Topic Sentence 2：__________________________________________
3．2．4 Topic：crime
Topic Sentence 1：__________________________________________
Topic Sentence 2：__________________________________________

Exercise 3-3
Directions： Read the following paragraphs and supply the missing topic sentence．
（1） ________________________________________________________________________________________________________________________
Iceland's flag， for instance， stands for features of the land．Red for the fire of Iceland's volcanoes． White is for ice． Blue is for the mountains． On India's flag， the blue wheel stands for peace and progress． The white stripe behind it is for truth． The black stripe on the flag of Malawi stands for the Negro people of that African land． The red stripe represents the blood they shed to free themselves from foreign rule．
（2） ________________________________________________________________________________________________________________________
The one most people are familiar with is the"desk dictionary"，sometimes refered to as general-purpose dictionary． Another kind is the pronouncing dictionary， which is concerned with a word's pronunciation more than with its meaning． A third type is the bilingual dictionary， which lists the words in one language and attempts to give equivalent meaning in another language． Other types include technical dictionaries， special purpose dictionaries，and scholarly dictionaries．


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