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在解答托福阅读插空题，首要任务就是要找到线索词。也就是能够让我们了解句子之间逻辑或者语法联系的词，线索词亦是解题的关键。下面就为大家分类分析一下线索词。
第一类：代词 eg. this, it, they
如果要插入的句子中有代词，可是代词所指代的内容又没有出现在句子本身，那么我们就可以根据代词的单复数等性质找到它指代的内容，再插入到该句之后。
For example:
Where would the sentence best fit?
This is a question that has puzzled scientists for ages.
Extinct but already fully marine cetaceans are known from the fossil record. How was the gap between a walking mammal and a swimming whale bridged? Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans. Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale.
看到了this，明显指代的是前文所提到的内容。再根据句子后半部分a question that has puzzled scientists for ages, 了解到this的指代内容原来是个question, 并且是科学难题呀。再看原文的四个插入点，第二个就明显很合适了。
第二类：名词 eg. 在句子中的形式一般为：this/these/such/another…+名词
如果句子中的线索词不是第一类的代词，而是以第二类的这种形式出现，那么这个最后的名词就是我们的线索词。这个名词一般会在原文已经出现过，我们要找到这个地方，再把句子插入适当的位置。之后要考虑句子插入后是否与插入口后面的句子保持正确的逻辑关系。
For example：
Where would the sentence best fit?
This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing.
the raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. The consequences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulverization of the soil. This is usually followed by the drying of the soil and accelerated erosion.
这里的线索词就是economic reliance,回去原文找根源，第二个插入口前面一句the raise of livestock is a major economic activity…，发现economic reliance就是major economic activity就是同义转换。但是这个时候不要过于着急把句子插进第二个插入口，你想一下啊，有可能作者在说这个topic的时候，有可能用了几个句子来阐述，所以要严谨一些，看看如果插入第二个口，和右边句子的意思是否能衔接。这个例子中，插入句子描写了一个不好的结果—overgrazing，而第二个插入口后一句话就是写了consequences of excessive grazing,因此逻辑上也是通顺的，可以安心地把句子放在第二个插入口啦!
第三类：逻辑词 eg.however/but /thus/accordingly/consequently/hence ...
以上两类线索词都是根据文中的语法联系来解题的，可是有些题目中的插入句没有这两类线索词，那么它的线索词就可能是一些表示因果、转折等各种逻辑关系的逻辑词，举例来说就是，however/but…这类表转折和 thus/accordingly …这类表因果关系的词，相信大家在写作的时候已经把这些词倒背如流了吧!这一类的插入题可能比前两类线索词的题要相对难一些，因为干扰项会比较强大，但是只要细心，理清前后句的逻辑关系，童鞋们还是可以攻克滴!
For example:
Where would the sentence best fit?
Consequently, tunas do not need to suck in water.
Because they are always swimming, tunas simply have to open their mouths and water is forced in and over their gills.Accordingly, they have lost most of the muscles that other fishes use to suck in water and push it past the gills. In fact, tunas must swim to breathe. They must also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant.
这个题目中，插入局句首的consequently就是一个表结果的线索词，表明前文所说的事情导致了tunas 不需要吸入水。我们看到第二个插入点的前一句话说，tunas张开嘴，水就会被推进他们的嘴里，如果把插入句放在这句后面逻辑上是十分连贯的。可是一些人会觉得第三个插入点也很合适，因为这个插入点的前一句说，tunas失去了其他鱼用来吸水的肌肉，如果后面说tunas不需要吸水貌似也合理，但是要注意，插入句用的是需要(need)，如果tunas失去了肌肉，那么就是不是需不需要，而是可不可以了。插入第二个插入点后，再检查下前后文的连贯，发现很适合。如果放在第三个插入点的话，和后文的衔接就会变得奇怪。因此，童鞋们要细心一些，记得检查!
总之，对于线索词我们可以得出一些搜索的常规套路，首先在插入的语句中找到线索词;然后，通读原文，找到满足线索词插入的地方;最后，瞻前顾后，检查插入后原文前后的逻辑和表达是否通顺。
以上就是小编整理的教你如何解答插空题的精彩内容希望可以帮助托福考生，更多精彩内容尽在，预祝托福考生取得理想成绩!