原句2: She tries to improve her looks.
斜體部分應(yīng)為主題句中的關(guān)鍵詞。她試著改變她面容的理由是什么？或者她采取什么方法來(lái)改善呢？我們無(wú)法從關(guān)鍵詞中清楚得知。
修正：She tries many ways to improve her looks.
修正：There are some reasons why she tries to improve her looks。
1.3 如何寫好主題句的中心思想
主題句由兩部分組成，即主題(topic)和中心思想（controlling idea）。中心思想的作用是導(dǎo)向(control)和制約(limit)。我們前面談到的關(guān)鍵詞就反映了中心思想。所謂導(dǎo)向就是規(guī)定段落的發(fā)展脈絡(luò)，所謂制約就是限制主題的覆蓋范圍，兩者不可分割。沒(méi)有導(dǎo)向，內(nèi)容就會(huì)離題或偏題；沒(méi)有制約，內(nèi)容就可能超出一個(gè)段落所能容納的范圍。
對(duì)于初學(xué)寫作的人來(lái)說(shuō)，“導(dǎo)向”的重要性容易理解，但如果由他們自己來(lái)構(gòu)思一個(gè)主題句，就可能忽視“制約”這一面。例如：
There are two ways in which one can own a book. The first is the property right you establish by paying for it, just as you have made it a part of yourself and the best way to make yourself a part of it is by writing in it.
本段的主題句如果沒(méi)有in which 引出的定語(yǔ)從句，那么two ways 不僅不能起制約作用，而且也不能起導(dǎo)向作用，句子本身讀起來(lái)也就使人覺(jué)得欠缺點(diǎn)什么。
Exercise is beneficial to your heart. A 22-year study was conducted by doctors in California. They found that people who work at physical jobs experience fewer heart attacks than other people. These active people work all the time at moderate speeds, their daily routine gives them an adequate amount of exercise and helps them stay in shape.
"Exercise is beneficial"這是毫無(wú)疑義的。但主題句中如不加上"to your heart"來(lái)加以 control 和 limit，那就流于空泛。
因此，緊緊把握主題句中controlling idea的導(dǎo)向和制約作用，是短文寫作成功關(guān)鍵之一。
2．推展句
2.1 主要推展句
主要推展句(major supporting statement)的主要特點(diǎn)是：圍繞段落主題句展開(kāi)的每一個(gè)推展句本身都不要求作進(jìn)一步的說(shuō)明或證明，句與句之間的關(guān)系是相互獨(dú)立又是互相連接的。
例1：(主題句) There are several factors affecting climate. (推展句1)One factor is the mount of sunlight received. (推展句2)Altitude, or the height above sea level, also determines climate. (推展句3)The oceans have an effect on the climate of adjacent land. (推展句4)In addition, climate is influenced by the general circulation of the atmosphere.