交作业。谢谢G兄！

据一项于12 月 8 日发表在Science Advances杂志上的研究的合著者、土壤生态学家Matthew Bowker表示，中国长城的土壤表面覆盖着一层由微小无根植物和微生物组成的“活皮”，即生物结皮，这是该遗产地持久力的来源。

Based on Matthew Bowker - a soil ecologist and the  co_author of a research published on December 8th's Science Advances magazin , the soil on China's Great wall is coverd by a living skin, so called Biological soil crusts,  which are composed of  rootless micro  plants and microorganism.  This is why this heritage can last so long.