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23.The hydrologic cycle，a major topic in this science，is thecomplete cycle of phenomena through which water passes，beginning asatmospheric water vapor，passing into liquid and solid form asprecipitation，thence along and into the ground surface，and finallyagain returning to the form of atmospheric water vapor by means ofevaporation and transpiration. 水文循环，作为该学科中的一个主要课题，指的是水所经过的诸现象的整个循环过程，开始时是作为大气中的水蒸气，转而作为雨、雪、露、雹一类的降水量经过液体和固体形态，由此而沿着地层表面分布或进入地层表面，最终通过蒸发和散发作用再度回复到大气水蒸气的形态。 24.The historian Frederick J. Turner wrote in the 1890s that theagrarian discontent that had been developing steadily in the UnitedStates since about 1870 had been precipitated by the closing of theinternal frontierthat is，the depletion of available new land neededfor further expansion of the American farming system. 史学家弗雷德里克.杰.特纳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。 25.In the early 1950s，historians who studied preindustrial Europe began， for the first time in large numbers，to investigate moreof the preindustrial European population than the 2 or 3 percent whocomprised the political and social elite：thekings，generals，judges，nobles，bishops，and local magnates who hadhitherto usually filled history books. | 
