说明
subject of gerund(动名词的逻辑主语)
核心问题
…where there are trees their roots break the soil up—allowing the rain to sink in and also bind the soil, thus preventing its being washed away easily. 如何分析句中的 its being washed?
词典解答
being washed 是动词 wash 的动名词被动式,作现在分词 preventing 的宾语,而 its (it 的物主代词) 是动名词 being washed 的逻辑主语,见 subject of gerund。