专题限时训练(三十五)[史地自然型阅读理解(二)](限时：25分钟)(一)Animalscanmovefromplacetoplace,butplantscannot.Whenananimalisunderattack,itcanrunawayorfightback.Plantscertainlycannotrunaway,andtheylackteethandclaws.Butplantscandefendthemselvesbyusingbothphysicalandchemicalmeans.Someplantshavetheirownwaystokeepanimalsaway.Forexample,theleavesofthehollyplanthavesharpspines(刺)thatdiscouragegrasseatinganimals.Hollyleavesonlowerbrancheshavemorespinesthanleavesonupperbranches.Thisisbecausethelowerleavesareeasierformostanimalstoreach.Someplants,suchastheoaktree,havethickandhardleavesthataredifficultforanimalstoeat.Somegrassesmaycontainasandymaterial;eatingsuchgrasseswearsdowntheanimal'steeth.Manyplantsalsohavechemicaldefenses.Someplantsproducechemicalsthattastebitterorcauseanunpleasantreaction.Someplantsmayfightagainstanattackbyincreasingtheproductionofthesechemicals.Whenacaterpillar(毛虫)bitesatobaccoleaf,theleafproducesachemicalmessenger.Thismessengersendstotherootstheinformationtoproducemorenicotine.Thehigherlevelsofnicotinediscouragethecaterpillar.Manyplantsdependonbothphysicalandchemicaldefenses.AcertainplantinChina,forinstance,hasprickly(多刺的)leaves,andeachpricklecontainspoisonousvenom(毒液).Asingleexperiencewiththiskindofplantwillteachananimaltostayawayfromitinthefuture.1．Thehollyplanthasmorespinesonthelowerleavesbecausemostanimals________．A．arenottallenoughB．likethelowerleavesonlyC．arenotcleverenoughD．cangetthelowerleaveseasily2．Todefendthemselves,oaktreesuse________．A．chemicalmeansB．physicalmeansC．bitterchemicalsD．sandymaterials3．Howdoestobaccoprotectitselfagainstanattackfromacaterpillar?A．Itsleavesfightagainsttheattackbyphysicalmeans.B．Itsrootssendamessengertodiscouragethecaterpillar.C．Itsrootsincreasetheproductionofnicotinewhenitisattacked.D．Itsleavesproducepoisonoussandtodrivethecaterpillaraway.4．Whatwouldbethebesttitleforthispassage?A．PlantsandanimalsB．HowplantsdefendthemselvesC．AttacksanddefensesD．Howanimalseatplantleaves(二)Ifyouareafraidofthedark，it'snotabigdeal.It'sperfectlynormaltofeelafraid.Afterall，animalsdo，too.“Fearmatters”，saysKarenWarkentin，anecologist.“It'sagoodthing”，sheadds,“becausefearmakesyoudothingsthatkeepyoualive.”Likekids，manyanimalsexperiencefearandtheyrespondtothefeelinginvarietyofways.Afrightenedturtlepullsitsheadandlegsinsideitsshell.Asmallfishwillswimawaywhenabig，hungryfishapproaches.Someanimalsrespondtofearinwaysyoumightnotexpect.Thefirstexampleisthatthefearofbeingeatencanscaresomefrogsrightoutoftheireggs.WarkentinmadethesurprisingdiscoverywhilestudyingredeyedtreefrogsinCostaRica.Inthisspecies，femalefrogsattachjellylikeclumps(果冻一样的块状物)oftheireggstotheundersidesofleaves.Theleaveshangonbranchesthatdangle(悬挂)overponds.Aftertheyhatchfromtheeggs，thetadpoles(蝌蚪)thenfallintothewater，wheretheyeventuallygrowintoadultfrogs.Treefrogeggsusuallygrowfor6daysbeforehatching.Iftheysensethatahungrysnakeisabouttoattack，however，theycanhatchupto2daysaheadoftheschedule.Asthesnakesareunabletoswim，byfallingintothewaterearly，thetadpolescanescape.Ifhatchingearlyhelpsprotectredeyedtreefrogsfromsnakes，youmightwonderwhytheireggsdon'talwayshatchsooner.Itturnsoutthathatchingearlybringsitsowndanger.Oncetadpoleslandinthewater，hungryfishandotheranimalsliketoeatthem,too.Stayingintheireggsfor6days，then，allowsfrogem...
