如果托福阅读文章中一句话与另一句话存在转折关系，通常要有表示转折的逻辑关系词，而且一般情况下语义重心都是转折后的内容。我们在分析句子间的转折关系前，要明确表示转折的逻辑词都有哪些。它们通常包括but ，yet ，however ，whereas ，on the contrary， contrary to ，in contrast等。当托福阅读修辞目的题中的定位句与前文存在转折关系时，通常作者的意图是反驳前文的某种观点或者否定前文的内容。
下面举两个例子进行具体分析。
例1：In Europe, before the introduction of the mechanical clock, people told time by sun (using, for example, shadow sticks or sun dials) and water clocks. Sun clocks worked, of course, only on clear days; water clocks misbehaved when the temperature fell toward freezing, to say nothing of long-run drift as the result of sedimentation and clogging. Both these devices worked well in sunny climates; but in northern Europe the sun may be hidden by clouds for weeks at a time, while temperatures vary not only seasonally but from day to night.
Why does the author provide the information that ”in northern Europe the sun may be hidden by clouds for weeks at a time, while temperatures vary not only seasonally but from day to night”?
○ To emphasize the variety of environments in which people used sun and water
clocks to tell time
○ To illustrate the disadvantage of sun and water clocks
○ To provide an example of an area where water clocks have an advantage over
sun clocks
○ To counter the claim that sun and water clocks were used all over Europe
托福阅读试题解析：
(1) 通过题干定位到文中最后一句话中but的后面，but一词表明后面的内容是与前面是转折关系，后面说：但是在北欧，太阳可能一下被乌云遮住几个星期，同时气温也不仅只随着季节变化，早晚也有温差。
(2) 定位句之前有转折，通常都是对前文的否定，所以看一下but前说了什么以明确否定的内容。前面说这两个设备在晴天时都能很好地工作。由此可以判断否定的对象应该就是这两个设备。
(3) 到底是哪两个设备呢? these提示我们要向前找，所以看一下上一句话，发现其中有个分号，可能分号前后各说一种设备。发现前面说的是太阳钟，后面说的是水钟，两个设备明确了。
(4) 结合这两句话，可以看出but后逗号前的内容正是对太阳钟的否定，逗号后面的内容正是对水钟的否定。因此答案为含有负面信息的B项。
例2：The undisputed pre-Columbian presence in Oceania of the sweet potato, which is a New World domesticate, has sometimes been used to support Heyerdahl’s “American Indians in the Pacific” theories. However, this is one plant out of a long list of Southeast Asian domesticates. As Patrick Kirch, an American anthropologist, points out, rather than being brought by rafting South Americans, sweet potatoes might just have easily been brought back by returning Polynesian navigators who could have reached the west coast of South America.
Why does the author mention the views of “Patrick Kirch”?(3)
○ To present evidence in favor of Heyerdahl’s idea about American Indians reaching Oceania
○ To emphasize the familiarity of Pacific islanders with crops from many different regions of the world
○ To indicate that supposed proof for Heyerdahl’s theory has an alternative explanation
○ To demonstrate that some of the same crops were cultivated in both South America and Oceania
解析：
(1) 题干问作者为什么提到PK这个人的观点。回到文中进行定位，发现最后的一整个长句说的就是PK的观点。提取一下主要信息点，PK的观点是：甘薯不是被南美洲人带来的，而可能仅仅是被到过南美的波利尼西亚人带回来的。
(2) 提到PK对甘薯来源的观点目的是什么呢?句首的as表示正像、正如，因此这句话与前面是一个顺承关系，前面说，但是这只是东南亚驯化的很多植物外的一种。句中的this提示我们还要向前看，并且句首的however表明后面的信息与前面是转折关系，而后一句话句首的as又表明与上一句话是顺承关系。由此判断出定位句与前文存在转折关系，所反驳的就应该是however之前的观点。
(3) 看however之前说了什么，这句话比较长，提取主要信息，主要说的是H的理论(太平洋岛上的人来源于美洲印第安)的证据是美洲驯化的甘薯出现在了大洋洲。
(4) 美洲印第安人也就是定位句中的南美州人，所以我们找到了however的转折点，前面说甘薯用来证明太平洋岛居民源于南美，后面说甘薯不是被南美洲人带来的，也就是说不能被用来证明太平洋岛居民源于南美。
(5) 综合以上分析，PK的观点就是为了说明之前支持H的理论的证据可能有误。所以，选择C项。
通过上面结合托福阅读试题和托福阅读文章段落的分析可以看出转折这种手法还是有很重要地位的，如果能提前发现这个手法那么对于大家理解托福阅读是很有帮助的。
