在托福阅读备考的过程中，除了对单词，长难句分析以及学术背景进行补充之外，10种托福阅读的基本题型也是大家准备的重点。毕竟就像去医院治病一样，能对症下药，当然会起到更好的效果。句子插入题本来属于10种题型中比较简单的类型，但是在对众多学生的课程教授过程之中，笔者发现，句子插入题的一个本质和一个原则往往被大家忽略，导致失分很多，希望大家引起重视。

　　PART1：一个本质---插入句是一句“可有可无”的话。

　　本题的出题位置大家比较清楚，一般处于倒数第二题的位置，并且用来出题的段落是大家应该在前面的题目中已经见到过，而之前的题目和文章既然大家理解起来没有出现大的障碍，就说明插入进来的句子是----一句可有可无的话。这就要从两个方面来理解了。

　　○何为“可有”?

　　既然插入句能放进原文中去，就说明它和原文是有一定关系的，所以叫“可有”，这也就意味着，插入句的部分含义是在原文中有所重复的。所以我们的重点是回到文中找那部分被重复的句意。例如：

　　█Watt's steam engine soon showed what it could do. █It liberated industry from dependence on running water. █The engine eliminated water in the mines by driving efficient pumps, which made possible deeper and deeper mining. █The ready availability of coal inspired William Murdoch during the 1790s to develop the first new form of nighttime illumination to be discovered in a millennium and a half. Coal gas rivaled smoky oil lamps and flickering candles, and early in the new century, well-to-do Londoners grew accustomed to gaslit houses and even streets. Iron manufacturers, which had starved for fuel while depending on charcoal, also benefited from ever-increasing supplies of coal: blast furnaces with steam-powered bellows turned out more iron and steel for the new machinery. Steam became the motive force of the Industrial Revolution as coal and iron ore were the raw materials.

　　(TPO6-Powering the Industrial Revolution)

　　Look at the four squares [█] that indicate where the following sentence could be added to the passage.

　　The factories did not have to go to the streams when power could come to the factories.

　　Where would the sentence best fit?

　　在上题中，“liberated industry from dependence on running water”和 “The factories did not have to go to the streams”句意便发生了重合。所以我们可以确定，文中第二句话的前后应该是我们可以选择的范围。

　　○何为“可无”?

　　这个便是经常被大家忽略的地方。既然这句话，可以省略，那么这个插入句究竟要符合什么特点呢?还是以上题为例，我们发现 “liberated industry from dependence on running water”和 “The factories did not have to go to the streams”句意发生了重合，那究竟应该把插入句放在第二个█还是第三个█呢?这时就需要分情况讨论了：

　　情况1：放在第二个█，也就是说我们认为插入句是和下文有关系，既然要符合“可无”这个本质，所以说插入句必须是对下文概括或者引出。

　　情况2：放在第三个█，也就是说我们认为插入句是和上文有关系，既然要符合“可无”这个本质，所以说插入句必须是对上文进一步解释。

　　综合以上两种情况，我们会发现，插入句要么总结引出下文，要么进一步解释上文。所以我们会发现，在插入题中，前一句的叙述范围应该总比后一句大。

　　根据上述内容，也就引出了我们需要注意的一个非常重要的做题原则：

　　PART2：一个原则

　　在插入题中，句子的叙述顺序遵循从大到小，从抽象到具体的原则。找到重复的句意后，按照大小顺序安置插入句的位置。

　　在上题中，“liberated industry from dependence on running water”的意思是解放了工厂对水流的依赖。 “The factories did not have to go to the streams”的意思是工厂不用去往河流的位置。显然前者说的更概括和抽象，后者更具体，所以按照从大到小的顺序，应该选择第二个█。

　　PART3：实践练习

　　Trade between the West and the settled and prosperous Chinese dynasties introduced new forms and different technologies. One of the most far-reaching examples is the impact of the fine ninth-century AD. Chinese porcelain wares imported into the Arab world. █So admired were these pieces that they encouraged the development of earthenware made in imitation of porcelain and instigated research into the method of their manufacture. █From the Middle East the Chinese acquired a blue pigment—a purified form of cobalt oxide unobtainable at that time in China—that contained only a low level of manganese. Cobalt ores found in China have a high manganese content, which produces a more muted blue-gray color. █In the seventeenth century, the trading activities of the Dutch East India Company resulted in vast quantities of decorated Chinese porcelain being brought to Europe, which stimulated and influenced the work of a wide variety of wares, notably Delft. █The Chinese themselves adapted many specific vessel forms from the West, such as bottles with long spouts, and designed a range of decorative patterns especially for the European market.

　　(TPO10-Chinese Pottery)

　　Look at the four squares [█]that indicate where the following sentence could be added to the passage.

　　Foreign trade was also responsible for certain innovations in coloring.

　　Where could the sentence best fit?

　　在上题中，我们发现，插入句的“certain innovations in coloring”与原文中的“the Chinese acquired a blue pigment”句意进行了重复，显然，插入句说的更概括，范围更大，所以根据从大到小的原则，应该选择第二个■。