托福听力中有哪四大类信号词?托福听力考试中，考生想要考好，首先得学会在听力中抓住关键词，那么托福听力中有哪四大类信号词呢?接下来就跟着小编一起来了解一下吧。
托福听力关键信息信号词：简单信号词
这一类信号词是属于最为简单的信号词，比如“Okay”, “Well”, “Now”, “But”, and “So”这些，具体来说：
1. Okay和Now一般用在不同话题或是关键信息之间的过度，比如：
But all the other elements, like the location or characters, might be modified for each audience. Okay. So what about fairy tales?
Take the Grand Canyon for instance. Now, we geologists thought we had a pretty good idea of how the Grand Canyon in the southwestern United States was formed.
2. Well一般用在回答一个问题之前，所以听到这个词后面往往就是解释，比如：
Um… and it was basically because of Uranium-Lead Dating. Why? Well, as everyone in this class should know, we usually look at the grain type within sandstone, meaning the actual particles in the sandstone, to determine where it came from. “But” and "So" are usually followed by a key point.
3. But和So后面一般会紧跟一个关键信息点。
托福听力关键信息信号词：词组短句
Let’s move on to ...
This brings me to my next point, which is….
So far we have have been looking at…. Now I’d like to….
So now that we've covered…
What … is all about is this…
上面这些词组或是短句句式也是比较常见的关键信息信号词，一般都具有很明显的承上启下过渡作用，同时也会把前后的关键信息key point或者话题topic很明显的提示给大家，也是考生比较容易抓住的一类信号词，下面给大家举几个例子：
All right folks, let’s continue our discussion of alternative energy sources and move on to what’s probably the most well-known alternative energy source--- solar energy.
What Aristotle’s ethical theory is all about is this: he’s trying to show you how to be happy—what true happiness is.
All right, so far we have been looking at some of the core areas of linguistics, like syntax, phonology, semantics. Now I’d like to talk about the branch of historical linguistics, and the comparison of several different languages, or the comparison of different stages of a single language.
托福听力关键信息信号词：重要观点理论提示
接下来的这类信号词是相当关键的，一般在听力素材中出现这类句式，就代表着接下来说话者要讲的会是比较重要的观点和理论，而类观点理论都是有很高几率成为出题点的，大家一定不能错过：
(观点opinion) I think, It appears that, It is thought that
(理论theory) In theory, the hypothesis is that
再来看几个实例：
Now, in theory, that would seem a great time to advertise, but maybe a research shows you’re wrong, that the customers who buy sports equipment tend not to give it as a holiday gift, but want to use it themselves.
Well, the current hypothesis is that these microorganisms produce a chemical that interacts with the oxygen in the air, creating conditions that lead to the formation of the low thick clouds we observed.
托福听力关键信息信号词：其它类型信号词
最后还有一些零散的信号词也需要大家记住，这类信号词用来表示对话内容之间逻辑关系的情况比较多，考生在听到后要能够区分出信号词涉及内容的逻辑关系，进行简单记录为之后的解题提供线索和参考，这些词有：
原因类：reasons (because, since)
结果类：results (as a result, so, therefore, thus, consequently)
举例类：examples (for example, such as)
比较类：comparisons (in contrast, than)
对比类：an opposing idea (on the other hand, however)
引申类：another idea (furthermore, moreover, besides)
并列类：a similar idea (similarly, likewise)
解释类：restatements of information (in other words, that is)
结论类：conclusions (in conclusion, in summary)
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