01、普通信号词
  该类信号词共包括8类，即表顺接和递进、表对比和转折、表相似、表排列次序、表强调作用、表最高级、比较级，表因果关系，表举例子和说明。
  表顺接和递进：also，furthermore，moreover，what is more，in addition…
  表对比和转折：however,but,by comparison,nonetheless,nevertheless…
  表相似：similarly，in other words，that is，put another way，as…
  表排列次序：first,second,finally,eventually,later,then,next…
  表最高级、比较级：more,most,-est,best,better,exclusively,extremely,superior,preferable…
  表因果关系：reason,cause,since,in that,as,because,thanks to,owing to…
  表举例和说明：for example,for instance,that is to say,such as,include,破折号…
  02、特殊信号词
  雅思阅读中的特殊的信号词，就是那些很容易识别的词。如大写字母开头的人名，地名，专有名词，以及特殊印刷体和黑体等，这些词在英语文章中显得尤为突出，往往也是题干中关键词的原词定位。
  EXAMPLE：
  the US Congress voted NASA$10 million per year for ten years to conduct a thorough search for the extra-terrestrial life.
  这句话出现了US Congress,NASA专有名词信号词，极有可能成为定位的讯息。
  一、表达客观结论
  例词：
  indicate that,point out,report that,demonstrate that…，
  suggest that,find out,conclude that,…
  考点：
  But Byers points out that the benefits of increased exercise disappear rapidly after training stops,so any improvement in endurance resulting from juvenile play would be lost by adulthood。
  解析：文章中定位人名就比较好找到答案。表达客观结论的信号词与人名同时出现时，就是考点出没的地方。
  二、特殊符号
  考点：
  In very significant cases of role change,e.g.from a soldier in the ranks to officer,from bachelor to married man,the change of role has to have a very obvious sign,hencerituals.
  解析：文中斜体的部分其实就是考察的考点，这里只要能判断，需要填写的单词是斜体部分，照抄过来就可以轻松拿分。
  三、表达主观观点
  例词：say,believe,argue that,maintain that,claim…
  考点：
  The UCSF researchers maintain that the simplest and most cost-effective action is to establish smoke-free work places,schools and public places.
  解析：这道分类题考察区分a finding和an opinion。表达个人观点(an opinion)带有一定的主观性，所用的信号词显然与客观事实发现(a finding)的有所区别。
  03、信号词的特点
  信号词具有代表性，指的是能够体现信号词所在句子的主要意思;信号词是一类出现频率不高的词，因为信号词可以很大程度上帮助考生缩小阅读范围，快而准定位答案并解题;当高频词被限定或者修饰之后，也可以作为信号词使用。也就是说当某些词原本是高频词，但是经过修饰或限定进而在原来内容上进行补充后，那么该词就变成了一个信号词。