Plantingtrees课件
日期：2010-06-10 06:01
floodsarepreventedWhatdoes“theGreatGreenWall”mean?Itmeansa“GreatWall”oftrees，sothesoilisn’teasilywashedawayThedeadleavesonthegroundalsokeepthewaterfromrunningawayThewaterthenstaysinoneplaceandisusedbythetreesintheforestsInthisway，andbetween400and1，sotheyhavebuiltanewGreatWallacrossthenorthernpartofthecountryHowlongandhowwideistheGreatGreenWall?Itis7，sodroughtdoesnotoftenhappenHowcanforestspreventflood?Thetreesintheforestscankeepraindropsfromhittingthesoildirectly，700kilometreswideWhyistheGreatGreenWallsoimportant?Becauseitwillstopthewindfromblowingtheearthaway，000kilometreslong，millionsoftreesWhyhasChinabuilttheGreatGreenWall?BecauseChinesepeopledonotwanttoseemorefloodsanddroughts，Lesson42TheGreatGreenWallSanbeishelter-forest（三北防护林）XinjiangQinghaiGansuNingxiaShaanxiLiaoningJilinHeilongjiangInnerMongoliaShanxiHebeiBeijingTianjinAnswerthequestionsHowdoforestshelppreventdrought?Theyhelptokeepwaterfromrunningaway，andstopthesandfrommovingtowardstherichfarmland，
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