有一句挺流行的话叫：当你不知道自己想要做什么的时候，至少要知道自己一定不想要做什么。这个原理其实就是‘排除法’，放在托福听力中就是，当你不知道正确答案是什么的时候，至少要知道哪些一定不是。排除法一直并且will always是最实用的方法。

排除选项就跟排雷一样，一不小心就可能把正确的给排出去了。但是，假如知道错误的选项设计的常见套路是不是可以在‘排雷’的时候多添几分淡定的气质呢?在了解常见错误选项的特点之前，要先温习一下托福听力对听力能力的考察。

托福听力总共有3大类题型，basic comprehension, pragmatic questions, connecting information，三大类题型可以再细分成为8种题型，即gist-purpose, gist-content, detail, function, attitude, organization, connecting connect, inferences。每一种题型对应ETS想要考察的考生的听力能力，其实也可以归纳对智商，情商和逻辑的考察。每一种题型对听力能力的要求都超越了‘放完听力只剩下几个认识的单词还存在脑海里’的阶段，尤其是主旨题的考察重点。但是，听力尚处于这个阶段的同学在做听力选择题的时候就会很容易落入ETS设下的‘圈套’，为什么呢?以TPO9 Lecture2为例。

下面是部分原文：

Lecturer: So since we're on the topic of global climate change and its effects, in Alaska, in the northern Arctic part of Alaska, over the last ... oh... thirty years or so, temperatures have increased about half a degree Celsius per decade, and scientists have noticed that there’s been a change in surface vegetation during this time. Shrubs are increasing in the "tundra".

………………………………………………….

And because of the cold temperatures, the tundra has two layers: top layer, which is called the active layer, is frozen in the winter and spring, but thaws in the summer. Beneath this active layer is a second layer called "permafrost", which is frozen all year around, and is impermeable to water.

…………………………………………………………………

OK? Now since the temperatures have been increasing in Arctic Alaska, the growth of shrubs has increased. And this has presented climate scientists with a puzzle...

………………………………………………………………….

Lecturer: Good question! And the answer is both. The size of the shrubs has increased and shrub cover has spread to what was previously shrub-free tundra. Ok, so what's the puzzle? Warmer temperatures should lead to increased vegetation growth, right? Well, the connection is not so simple. The temperature increase has occurred during the winter and spring, not during the summer. But the increase in shrubs has occurred in the summer. So how can increase temperatures in the winter and spring result in increased shrub growth in the summer?

Well, it may be biological processes that occur in the soil in the winter, that cause increased shrub growth in the summer, and here's how: there are "microbes", ..……………………………………..And it allows the temperature of the soil to remain warm enough for microbes to remain active. So there's been increased nutrient production in the winter. And that's what's responsible for the growth of shrubs in the summer and their spread to new areas of the tundra. Areas with more new nutrients are the areas with the largest increase in shrubs.

……………………………………………………………………………………

Female student: But will it be long-term? I mean maybe the shrubs will be abundant for a few years, and then it'll change back to tundra.

Lecturer: Well, shrub expansion has occurred in other environments, like semiarid grassland, and tall grass prairies. And shrub expansion in these environments does seem to persist, almost to the point of causing a shift. Once is established, shrub land thrives, particularly in the Arctic, because Arctic shrubs are good at taking advantage of increased nutrients in the soil, better than other Arctic plants.

这篇讲座的结构是解释原因型，再准确一点是属于原因探索型，因为并不是直接给出比较确定的原因，正确答案是A，可以参考文中划线部分。下面就以这篇讲座的主旨题为例分析错误选项，关键词已经划出。

What is the lecture mainly about?

A, Factors involved in the increased growth of shrubs in Arctic Alaska

B, How temperature increases might be affecting the permafrost in Arctic  Alaska

C, Why nutrient production of microbes in the soil in Arctic Alaska is declining

D, Reasons that grasslands are turning into tundra in Arctic Alaska

那么BCD三个选项分别错在什么地方呢?

首先，B选项，我们可以挑出关键词temperature increases, the permafrost, 这些都是在听力原文中出现过的，但是这两个关键词再加上How和affect就构成典型错误选项即关键词乱拼，这也是逻辑混乱的一个结果，温度上升没有影响permafrost，而是the growth of shrubs。

其次，C选项，关键词nutrient production of microbes，找到关键词在原文中的位置我们会发现，这个nutrient是增加的，那么这个选项错误的原因就是与原文相悖了。

，选项D，关键词grassland一直到才出现，这样一个跑龙套的关键词怎么可以担当起概括文章主旨的重任呢，这个也是主旨题非常经典的错误选项即拿细节滥竽充数。

再以TPO18 L2 讲Roman sculpture的一篇讲座为例。(由于篇幅有限将不贴原文)

What is the lecture mainly about?

A, Different views of a type of sculpture popular in ancient Roman times

B, Evidence that Romans had outstanding artistic ability

C, The differences between Greek sculpture and Roman sculpture

D, The relationship between art and politics in ancient Roman times

这篇讲座属于观点挑战型，正确答案是A。对照原文分析一下BCD选项不难发现B选项是与原文相悖的，原文中说的是：Roman artists lacked creativity and skill especially compared to the Greek artists who came before them. 再来说C选项，Greek sculpture和Roman sculpture都在原文中提到过，但是再加上difference就出现逻辑混乱了，原文中说的是抄袭的问题。是D选项，关键词art，politics，relationship，关键词politics原文并没有提到，但是是对包含关键词empire，emperor的内容的概括，而这些只在部分出现，只是其中一个细节。