插入句子题是托福阅读的必考题型之一，基本一篇文章一个，一般放在倒数第二个题型。刚开始接触托福阅读的同学在做这个题型的时候往往心里慌得很，对着段落里面的四个小黑框无从下手。

　　下面我们就详细地讲一讲到底该如何把要插入的句子放入合适的小黑框。插入句子题着重考查的是句间的逻辑关系，也就是考生能否分析清楚段落里面句子和句子之间是如何衔接的。插入句子题常考查的句间衔接方式主要有三种：

　　The first种：指代衔接

　　这种衔接方式是最简单的一种，做题碰上的话基本不会给考生造成障碍，只需要搞清楚指代词指代什么基本就能得出正确答案。

　　我们以TPO19 Passage2Question13为例：

　　Although the ecosystem concept was very popular in the 1950s and 1960s, it is no longer the dominant paradigm. ■ Gleason's arguments against climax and biome are largely valid against ecosystems as well. ■ Furthermore, the number of interactions is so great that they are difficult to analyze, even with the help of large computers. Finally, younger ecologists have found ecological problems involving behavior and life-history adaptations more attractive than measuring physical constants. ■ Nevertheless, one still speaks of the ecosystem when referring to a local association of animals and plants, usually without paying much attention to the energy aspects. ■

　　要插入的句子：They may be more interested in researching, for example, the adaptations that some aquatic animals undergo to survive in dry desert environments.

　　句子里出现的指代词是they，而且说他们可能对研究更感兴趣，那说明前句应该要提到很多人，然后接着说they才比较符合行文逻辑。四个黑框前句有提及很多人的只有第三个黑框前句出现了younger ecologists，所以答案就是第三个黑框。

　　第二种：逻辑衔接

　　这种衔接比指代衔接难度系数稍微大一点，需要考生知道常见的一些逻辑关系，包括因果，转折，递进等。

　　我们以TPO15 Passage1 Question12为例：

　　Leatherbacks keep their body heat in three different ways. The first, and simplest, is size. The bigger the animal is, the lower its surface-to-volume ratio; for every ounce of body mass, there is proportionately less surface through which heat can escape. An adult leatherback is twice the size of the biggest cheloniid sea turtles and will therefore take longer to cool off. Maintaining a high body temperature through sheer bulk is called gigantothermy. ■It works for elephants, for whales, and, perhaps, it worked for many of the larger dinosaurs. ■It apparently works, in a smaller way, for some other sea turtles. ■Large loggerhead and green turtles can maintain their body temperature at a degree or two above that of the surrounding water, and gigantothermy is probably the way they do it. ■Muscular activity helps, too, and an actively swimming green turtle may be 7°C (12.6°F) warmer than the waters it swims through.

　　要插入的句子：However, these animals have additional means of staying warm.

　　句子里面出现了转折的逻辑关系，也就意味着这句话的前句和这句话的后句应该是在讲不一样的保持温暖的方法。分析整段我们会发现第四个黑框前面都是在讲gigantothermy这种方法，后面在讲肌肉活动也能够帮助保持温暖，那要插入的句子放在第四个黑框是最合适的。

　　第三种：语义衔接

　　这种衔接方式难度系数很大规模。不像指代衔接和逻辑衔接会有比较明显的信号词，它需要考生完全理解要插入的句子和段落原文。碰到这种衔接方式需要记得插入的句子作用都是承前启后。

　　我们以TPO11 Passage3 Question13为例：

　　Many signals that animals make seem to impose on the signalers costs that are overly damaging. ■A classic example is noisy begging by nestling songbirds when a parent returns to the nest with food. ■These loud cheeps and peeps might give the location of the nest away to a listening hawk or raccoon, resulting in the death of the defenseless nestlings. ■In fact, when tapes of begging tree swallows were played at an artificial swallow nest containing an egg, the egg in that “noisy” nest was taken or destroyed by predators before the egg in a nearby quiet nest in 29 of 37 trials. ■

　　要插入的句子：The cheeping provides important information to the parent, but it could also attract the attention of others.

　　这句话的意思是说吱吱的叫声提供重要的信息给父母，但是也会吸引其他动物的注意。插入的句子承前启后也就意味着前句要出现parent，后句要出现其他的动物。回到段落里面我们发现第二个黑框前面出现了a parent，后面出现了a listening hawk or raccoon，那显然放第二个黑框最合适。

　　以上就是托福阅读插入句子题常见的三种句间衔接方式，大家以后再拿到插入句子题就可以先冷静分析是哪一种衔接方式然后再选择合适的黑框了。

更多托福考试干货敬请关注新航道托福考试频道