难句类型：复杂修饰、插入语、省略
解释：beginning开始的一系列分词都是修饰主语The hydrologic cycle的，分别是beginning/passing/passing/returning。值得注意的是，thence along and into the grund surfacee 是thence passing along and entering into the ground surfacee的省略形式，但是看上去意思却很清楚。类似这样的省略，是出题者合理地利用了省略来达到改编学术论文时压缩文章篇幅的目的。
意群训练：The hydrologic cycle，a major topic in this science，is the complete cycle of phenomena through which water passes，beginning as atmospheric water vapor，passing into liquid and solid form as precipitation，thence along and into the ground surface，and finally again returning to the form of atmospheric water vapor by means of evaporation and transpiration.
34. Only when a system possesses natural or artificial boundaries that associate the water within it the hydrologic cycle may the entire system properly be termed hydrogeologic.（4） 只有当一个系统拥有自然的或人工形成的边界来把边界中的水与水文循环联系起来的时候，才有可能把整个的系统恰当的成为与水文地质学有关。
难句类型：复杂修饰、倒装
解释：only放在句首时，主句的情态动词may倒装，这是我们高中就已经学过的东西。然而句首的only与倒装的may距离如此之远，这在以前却没有见过，所以读上去让人不习惯。另外一个难点在于，前面的由when所引导的时间状语从句中，宾语boundaries后面跟了一个定语从句，that associate the water within it with the hydrologic cycle,而且从句中的associate with又被water within it所分开，读者还要分神去考虑it所指的是什么，所以读到后面倒装的may的时候，难免不知所云。
意群训练：Only when a system possesses natural or artificial boundaries that associate the water within it with the hydrologic cycle may the entire system properly be termed hydrogeologic.
35. The historian Frederick J. Turner wrote in the 1890’s that the agrarian discontent that had been developing steadily in the United States since about 1870 had been precipitated by the closing of the internal frontier--that is，the depletion of available new land needed for further expansion of the American farming system. （4） 史学家弗雷德里克.杰.特纳（Frederick J.Turner）于十九世纪九十年代著述道，美国约自18世纪70年代以来一直在持续不断发展的农民不满，由于国内边远地区（internal frontier）的封闭而更趋加剧--亦即是说，美国农业系统进一步扩展所必需的可资利用的新土地几近耗竭。
难句类型：复杂修饰
解释：典型的句子套句子。主句是F.J.T. wrote that，宾语从句中主干是the agrarian discontent had been precipitated by the closing of the internal frontier，在从句的主语the agrarian discontent后面又来了一个定语从句。
意群训练：The historian Frederick J. Turner wrote in the 1890’s that the agrarian discontent that had been developing steadily in the United States since about 1870 had been precipitated by the closing of the internal frontier--that is，the depletion of available new land needed for further expansion of the American farming system
36. In the early 1950’s，historians who studied preindustrial Europe （which we may define here as Europe in the period from roughly 1300 to 1800） began， for the first time in large numbers，to investigate more of the preindustrial European population than the 2 or 3 percent who comprised the political and social elite：the kings，generals，judges，nobles，bishops，and local magnates who had hitherto usually filled history books. （4） |
