很多刚刚接触雅思大作文的同学在撰写主体段的时候常常会犯这样一个问题：缺少主题句。我们先来看下面的内容，思考下这段内容有没有什么问题。
I need a water bottle for hike in case I get thirsty. A raincoat is useful when it rains. A compass will help me go in the right direction. Sandwiches will be an easy-to-carry snack. I can use a camera to take photos of attractive places.
通过阅读发现，这几个句子共介绍了5个物品不同的功能，但句子之间没有联系，各自为阵。因此，这样的句子即使堆砌在一起，也不能称之为写作中的paragraph，因为对paragraph的定义是：
A paragraph is a self-contained unit of a discourse in writing dealing with a particular point or idea. A paragraph consists of one or more sentences.
围绕一个特定的观点进行展开称之为段落。
因此，我们在撰写大作文的时候，如果段落中也都是充斥着松散的句子，考官无法把握段落在论证什么。这时我们需要给它增添一个特定的观点，即主题句的存在。比如上面的五个物品总结下共性都是旅行或者远足需要用到的东西，我们可以添加这样的一个句子作为主题句：I will prepare some items for my hike.
什么是主题句
Topic sentences helps organize the paragraph by summarizing the information in the paragraph and connect to an essay’s thesis statement. In formal writing, the topic sentence is usually the first sentence in a paragraph.
主题句是对立场的支持和拓展，同时总结一个段落主旨的句子；它通常写在段落的首句。
👉拿一道题目举个例子：
In many cities, problems related to overpopulation are becoming more common. Some governments are now encouraging businesses and individuals to move out of cities to rural areas. Do the advantages of this trend outweigh the disadvantages?
Firstly, this is related to living standards. Residents of cities typically enjoy better medical care, employment opportunities, and entertainment options. For instance, a person who moves from New York City to upstate New York is likely to recognize an immediate decline in their daily quality of life. Secondly, there may be significant economic issues. Cities tend to be the economic centers of any given state or nation. By reducing the concentration of industry in urban areas, there is some likelihood that innovation will be negatively impacted as the pool of potentially competent employees disperses.
这部分内容围绕两个方面展开，第一个方面是对城市居民的生活有影响，第二个方面是对企业的创新力有阻碍。因此，我们可以得出主题句：This initiative can harm businesses and residents.
主题句写法
了解了含义之后，我们来进一步学习如何写出一个合格的主题句。
主题句由两部分构成：topic+central idea
topic是你的立场，即要写段落围绕的话题。在写的时候可以适当改写。
比如刚才的题目In many cities, problems related to overpopulation are becoming more common. Some governments are now encouraging businesses and individuals to move out of cities to rural areas. Do the advantages of this trend outweigh the disadvantages?
这道题中的topic本身应该是In many cities, problems related to overpopulation are becoming more common. 但这个句子如果作为主题句的一部分会导致句子过长，因此我们可以直接用政策/方案/策略来作为替代，即this initiative
central idea是针对立场的个人看法，比如它的优点缺点是什么，或者它是由什么原因产生的。
比如：
【topic】Dogs make wonderful pets because they help you to 【central idea】live longer.
【topic】physical activities results in 【central idea】healthy post-workout glow.
【topic】Crime in poverty-stricken areas occurs as a result of 【central idea】systemic discrimination.
再来看刚才的题目：
主题句的topic：this initiative
我们把central idea 增添进去：harm businesses and residents.
最后的主题句即为This initiative can harm businesses and residents.
注意⚠️：
1. 保证你的central idea一定是比较具体的，不能太过宽泛。比如如果我把刚才的主题句改为this initiative has many benefits 那就是一个无效的central idea，因为没有对立场起到进一步拓展的作用，要给出具体的好处是什么。
2. 每个主体段的central idea不能有重复，否则会导致后面对主题句的拓展会有相似的论证，这在写作中是大忌。
常用表达
topic和central idea之间通常会用一些表积极/消极意义或者表原因的动词进行连接。
比如：
👉有利于
help/motivate/enhance/improve/boost…、
be beneficial to /it is beneficial to…、
contribute to…、
exert a positive influence/impact/effect on…、
… is a boon
👉不利于
harm/decrease/hamper/..
be detrimental to…、
pose a threat to…
👉原因
because/because of…
since…
thanks to (the fact that)/due to (the fact that) /owing to (the fact that)…
… caused by…
本文作者
TD福利
以上内容为主题句的详细写法，为了帮助同学们进一步巩固学习，我们还为大家准备了一些经典题目的练习和对应的参考示范。想要获得资料的同学可以发送暗号「主题句」联系马甲获取哦！
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