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1、TPO1Reading1TimberlineVegetationonMountains2Reading2TheOriginsofTheater5Reading3Groundwater8Reading1TimberlineVegetationonMountains Thetransitionfromforesttotreelesstundraonamountainslopeisoftenadramaticone.Withinaverticaldistanceofjustafewtensofmeters,treesdisappearasalif
2、e-form(树木这种生命形式消失了）andarereplacedbylowshrubs,herbs,andgrasses.Thisrapidzoneoftransitioniscalledtheuppertimberlineortreeline.Inmanysemiaridareasthereisalsoalowertimberlinewheretheforestpassesintosteppeordesertatitsloweredge,usuallybecauseofalackofmoisture.Whichofthefollowing
3、canbeinferredfromparagraph1aboutboththeupperandlowertimberlines? ○Botharetreelesszones. √○Bothmarkforestboundaries. ○Botharesurroundedbydesertareas. ○Bothsufferfromalackofmoisture.本题需要整体与部分分析，第一句为总起句，theupperandlowertimberlines都属于mountainslope. Theuppertimberline,liket
4、hesnowline,ishighestinthetropicsandlowestinthePolarRegions.ItrangesfromsealevelinthePolarRegionsto4,500metersinthedrysubtropicsand3,500-4,500metersinthemoisttropics.Timberlinetreesarenormallyevergreens,suggestingthatthesehavesomeadvantageoverdeciduoustrees(thosethatlosethei
5、rleaves)intheextremeenvironmentsoftheuppertimberline.Therearesomeareas,however,wherebroadleafdeciduoustreesformthetimberline.Speciesofbirch,forexample,mayoccuratthetimberlineinpartsoftheHimalayas. Attheuppertimberlinethetreesbegintobecometwistedanddeformed.Thisisparticular
6、lytruefortreesinthemiddleandupperlatitudes,whichtendtoattaingreaterheightsonridges,whereasinthetropicsthetreesreachtheirgreaterheightsinthevalleys.Thisisbecausemiddle-andupper-latitudetimberlinesarestronglyinfluencedbytheduration（持续时间）anddepthofthesnowcover.(Asthesnowisdeep
7、erandlastslongerinthevalleys,treestendtoattaingreaterheightsontheridges,eventhoughtheyaremoreexposedtohigh-velocitywindsandpoor,thinsoilsthere.Inthetropics,thevalleysappeartobemorefavorablebecausetheyarelesspronetodryout,theyhavelessfrost（霜）,andtheyhavedeepersoils.According
8、toparagraph3,whichofthefollowingistrueoftreesinthemiddleandupperlatitudes? √○Tree
