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1、.TPO1Reading1TimberlineVegetationonMountains2Reading2TheOriginsofTheater5Reading3Groundwater8..Reading1TimberlineVegetationonMountains Thetransitionfromforesttotreelesstundraonamountainslopeisoftenadramaticone.Withinaverticaldistanceofjustafewtensofmeters,t
2、reesdisappearasalife-form(树木这种生命形式消失了）andarereplacedbylowshrubs,herbs,andgrasses.Thisrapidzoneoftransitioniscalledtheuppertimberlineortreeline.Inmanysemiaridareasthereisalsoalowertimberlinewheretheforestpassesintosteppeordesertatitsloweredge,usuallybecauseof
3、alackofmoisture.Whichofthefollowingcanbeinferredfromparagraph1aboutboththeupperandlowertimberlines? ○Botharetreelesszones. √○Bothmarkforestboundaries. ○Botharesurroundedbydesertareas. ○Bothsufferfromalackofmoisture.本题需要整体与部分分析，第一句为总起句，theupperandlowertim
4、berlines都属于mountainslope. Theuppertimberline,likethesnowline,ishighestinthetropicsandlowestinthePolarRegions.ItrangesfromsealevelinthePolarRegionsto4,500metersinthedrysubtropicsand3,500-4,500metersinthemoisttropics.Timberlinetreesarenormallyevergreens,sugge
5、stingthatthesehavesomeadvantageoverdeciduoustrees(thosethatlosetheirleaves)intheextremeenvironmentsoftheuppertimberline.Therearesomeareas,however,wherebroadleafdeciduoustreesformthetimberline.Speciesofbirch,forexample,mayoccuratthetimberlineinpartsoftheHimal
6、ayas. Attheuppertimberlinethetreesbegintobecometwistedanddeformed.Thisisparticularlytruefortreesinthemiddleandupperlatitudes,whichtendtoattaingreaterheightsonridges,whereasinthetropicsthetreesreachtheirgreaterheightsinthevalleys.Thisisbecausemiddle-andupper
7、-latitudetimberlinesarestronglyinfluencedbytheduration（持续时间）anddepthofthesnowcover.(Asthesnowisdeeperandlastslongerinthevalleys,treestendtoattaingreaterheightsontheridges,eventhoughtheyaremoreexposedtohigh-velocitywindsandpoor,thinsoilsthere.Inthetropics,the
8、valleysappeartobemorefavorablebecausetheyarelesspronetodryout,theyhavelessfrost（霜）,andtheyhavedeepersoils.Accordingtoparagraph3,whichofthefollowingistrueoftreesinthemiddleandupperlatitudes? √○T
