ide in combating dental decay is well established and, without a doubt, socially beneficial. However, fluoride's toxic properties have been known for a century. In humans excessive intake ( for adults, over 4 milligrams per day) over many

years can lead to skeletal fluorosis, a well-defined skeletal disorder, and in some plant species, fluoride is more toxic than ozone, sulfur dioxide, or pesticides.

文章开始说“氟在抗牙腐蚀方面的功效是众所周知的，并且毫无疑问（without a doubt）是有其社会益处的”，由without a doubt可知这是让步，所以后面马上作出转折，提到它的毒性，“但是，氟的毒性为人们所知已有一个世纪之久了”，这才是文章的重点。

由此可见，有让步就有转折。那么如何应对阅读中的这种“让步逻辑”呢？首先要注意：在“让步——转折”结构中，转折之后是重点，应该多加关注，而让步部分是铺垫，可以速读。

综上所述，GRE考试不过是单词与逻辑的游戏而已。如上所示，谁理解了游戏规则并遵循这些规则备考，谁就将获得理想的分数。