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下半年托福考试阅读理解模拟冲刺题.docx

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下半年托福考试阅读理解模拟冲刺题2017下半年托福考试阅读理解模拟冲刺题导语：阅读理解是托福考试中篇幅最长的，但是它并没有想象中可怕，下面是YJBYS小编提供的2017下半年托福考试阅读理解模拟冲刺题，做完记得对答案哦!Pheromonesaresubstancesthatserveaschemicalsignalsbetweenmembersofthesamespecies.Theyaresecretedtotheoutsideofthebodyandcauseotherinpidualsofthespeciestohavespecificreactions.Pheromones,whicharesometimescalled"socialhormones,"affectagroupofinpidualssomewhatlikehormonesdoaninpidualanimal.Pheromonesarethepredominantmediumofcommunicationamonginsects(butrarelythesolemethod).Somespecieshavesimplepheromonesystemsandproduceonlyafewpheromones,butothersproducemanywithvariousfunctions.Pheromonesystemsarethemostcomplexinsomeoftheso-calledsocialinsects,insectsthatliveinorganizedgroups.Chemicalcommunicationdiffersfromthatbysightorsoundinseveralways.Transmissionisrelativelyslow(thechemicalsignalsareusuallyairborne),butthesignalcanbepersistent,dependinguponthevolatilityofthechemical,andissometimeseffectiveoveraverylongrange.Localizationofthesignalisgenerallypoorerthanlocalizationofasoundorvisualstimulusandisusuallyeffectedbytheanimal'smovingupwindinresponsetothestimulus.Theabilitytomodulateachemicalsignalislimited,comparedwithcommunicationbyvisualoracousticmeans,butsomepheromonesmayconveydifferentmeaningsandconsequentlyresultindifferentbehavioralorphysiologicalresponses,dependingontheirconcentrationorwhenpresentedincombination.Themodulationofchemicalsignalsoccursviatheelaborationofthenumberofexocrineglandsthatproducepheromones.Somespecies,suchasants,seemtobeveryarticulatecreatures,buttheirmediumofcommunicationisdifficultforhumanstostudyandappreciatebecauseofourownolfactory,insensitivityandthetechnologicaldifficultiesindetectingandanalyzingthesepheromones.Pheromonesplaynumerousrolesintheactivitiesofinsects.Theymayactasalarmsubstances,playaroleininpidualandgrouprecognition,serveasattractantsbetweensexes,mediatetheformationofaggregations,identifyforagingtrails,andbeinvolvedincastedetermination.Forexample,pheromonesinvolvedincastedeterminationincludethe"queen