Nature、physical为原词复现的关系,G项中的mental health与下文中的reduce depression相照应。37.B。本段中的National parks contain forested areas that not only protect water sources.by preserving wetlands介绍了国家公园有助于减少自然灾害所产生的危害,因此B项可以概括本段的主旨大意。3&.F。上文中的This can save lives and infrastructure by preventing landslides,.avalanches anderosion..These areas also reduce floods by preserving wetlands与F项并列,具体解释了国家公园可以降低哪些自然灾害所带来的影响。39.E。E项与上文中的ln2015,4 million visitors at Yellowstone National Park generatednearly $500 million dollars in spending,leading to 7,735 jobs and $225 million in income forworkers为语义上的顺承关系,具体解释了国家公园对经济的影响。上文中的jobs与E项中的jobs是原词复现的关系。