托福閱讀：句子插入題的三種邏輯

1. 轉(zhuǎn)折關(guān)系
　　一旦給定句中出現(xiàn)轉(zhuǎn)折關(guān)系，就意味著該句的前后文內(nèi)容存在反義。如下例：
　　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.
　　However, these animals have additional means of staying warm.
　　從給定句的語(yǔ)義不難看出，該句后文必然要提到某種保暖的方法。而從however引導(dǎo)的轉(zhuǎn)折邏輯和additional可以想到，這是一種“額外”的方法，也就意味著在該句前文已經(jīng)提到過(guò)另一種保暖方法。通讀原文，可以發(fā)現(xiàn)只有空格4符合要求（前有g(shù)igantothermy，后有muscular activity）。

2. 因果關(guān)系
　　一旦給定句中出現(xiàn)因果關(guān)系，就意味著該句是原文中某句的原因（一般在原文句前）或結(jié)果（一般在原文句后）。如下例：
　　■ Another task for the Glomar Challenger’s scientists was to try to determine the origin of the domelike masses buried deep beneath the Mediterranean seafloor. ■ These structures had been detected years earlier by echo-sounding instruments, but they had never been penetrated in the course of drilling. ■ Were they salt domes such as are common along the United States Gulf Coast, and if so, why should there have been so much solid crystalline salt beneath the floor of the Mediterranean? ■
　　Thus, scientists had information about the shape of the domes but not about their chemical composition and origin.
　　從給定句的語(yǔ)義不難看出，該句描述的是某種科學(xué)研究方法，能讓科學(xué)家了解到dome的形狀，但無(wú)法獲知其化學(xué)成分和起源，而這種方法的出現(xiàn)應(yīng)該在該句前面。通讀全文，不難發(fā)現(xiàn)空格3前提及曾使用echo-sounding instruments（回聲探測(cè)設(shè)備），但沒(méi)有經(jīng)過(guò)drilling（鉆探），完全符合要求。

3. 遞進(jìn)關(guān)系
　　與轉(zhuǎn)折和因果相比，遞進(jìn)是一種許多考生都感覺(jué)比較陌生的邏輯關(guān)系。它表示的是后文在前文基礎(chǔ)上在語(yǔ)義上更加深入。但無(wú)論如何深入變化，后文也無(wú)法脫離前文的基礎(chǔ)，也就是說(shuō)前后文的主題應(yīng)保持基本一致，這點(diǎn)和并列關(guān)系類(lèi)似。所以在句插題的給定句中一旦出現(xiàn)遞進(jìn)關(guān)系，就意味著該句的關(guān)鍵詞必然能在原文中某處找到復(fù)現(xiàn)，從而插入復(fù)現(xiàn)句子后面的空格。如下例：
　　Transportation was becoming less of a problem for those who wished to move west and for those who had farm surpluses to send to market. ■Prior to 1815, western farmers who did not live on navigable waterways were connected to them only by dirt roads and mountain trails. ■Livestock could be driven across the mountains, but the cost of transporting bulky grains in this fashion was several times greater than their value in eastern markets. ■The first step toward an improvement of western transportation was the construction of turnpikes. ■These roads made possible a reduction in transportation costs and thus stimulated the commercialization of agriculture along their routes.
　　In fact, goods could be shipped more cheaply across the much greater distance of the Atlantic Ocean than they could from western New York to coastal cities.
　　不難發(fā)現(xiàn)，if fact就是一個(gè)典型的遞進(jìn)連詞。該句中提及more cheaply，所以其前句必然也會(huì)出現(xiàn)和價(jià)格或成本相關(guān)的內(nèi)容。通讀全文，可見(jiàn)空格3前居中出現(xiàn)cost of transporting，符合要求。