托福写作需要很多词汇，抽象词也是托福写作准备中不可忽视的一种词汇。下面由新航道的沈阳托福培训小编为您解答！

　　Periodic

　　用法：①ADJ.Periodiceventsorsituationshappenoccasionally，atfairlyregularintervals.

　　例句：Theyespeciallyemphasizedtheneedfornatural，serenesettingswherehurriedurbandwellerscouldperiodicallyescapefromthecity.(2002-01)

　　例句：ThisperiodicextinctionmightbeduetointersectionoftheEarth’sorbitwithacloudofcomets，butthistheoryispurelyspeculative.(2002-08)

　　例句：Periodically，moltenmaterialwellsoutoftheEarth’sinteriortoinvadethesurfacelayersortoflowontothesurfaceitself.Thismaterialcoolsintoawidevarietyofigneousrocks.(1999-01)

　　例句：Thewoollymammoth，along-hairedrhinoceros，andothermammalshavebeenperiodicallyexposedinthetundraofSiberia，thehairandredfleshstillfrozenincoldstorage.(1997-12)

　　例句：Periodicexhibitionsofthemembers’paintingsalsoincludedworksbynotedEnglishartistsoftheday，borrowedfromembryonicprivatecollectionsinthecity.(1999-10)

　　Peripheral

　　用法：①ADJ.Aperipheralactivityorissueisonewhichisnotveryimportantcomparedwithotheractivitiesorissues.

　　例句：Over100desistarestaripheran.(2000-01)

　　②ADJ.Peripheralareasoflandareoneswhichareontheedgeofalargerarea.

　　例句：Thesearethecentralnervoussystem(thenervecordmentionsabove)，consistingofthebrainandspinalcord，andtheperipheralnervoussystem，consistingofthecranial，spinal，andperipheralnerves，togetherwiththeirmotorandsensoryendings.

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