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.
