【阅读理解Withouttheatmospheretherewouldhenoweathernowindrainsnoworclouds.Airisallaroundus;weliveatthebottomofagreatoceanofair.Itisinvisiblebutwecanfeelitwhenitmoves.Therearemiles】

　　阅读理解

　　Withouttheatmospheretherewouldhenoweathernowindrainsnoworclouds.Airisallaroundus;weliveatthebottomofagreatoceanofair.Itisinvisiblebutwecanfeelitwhenitmoves.Therearemilesofairaboveuspressingdownwithgreatweightontheearthandeverythingonit.Becauseairpressesdownonusfromalldirectionsatthesametimeandbecauseweareabletobear(忍受)thisweightwedonotseemtofeelit.Butscientistshaveprovedthatairhasthisweightandthatanythingthathasweightcreates(产生)aforcecalledpressure.Aschangesinairpressuretakeplacetheymakeairmove.

　　Airisagasthatexpands(膨胀)whenheatedgetslighterandmovesupward.Whenairiscooleditgetsheaviersinksclosetotheearth'ssurfaceandflowslikewaterinagreatriver.Aswarmairrisescoldairrushesintotakeitsplace.Thuswindsoriginate(起源).Thewindsthatblowhighaboveusarecausedbythewarmerairrunningawayfromcolderair.Thewindwefeelneartheearth'ssurfaceistheheavycolderairtryinghardtocatchthewarmerair.Changesintemperaturecausetheairtomove.Andofcoursetherearemanychangessoairmovementsaretakingplacepracticallyallthetime.

　　1．Thefirstparagraphmainlytellsusthecausesof________.

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　　A．whywedon'tfeelair

　　B．whyatmosphereisimportanttous

　　C．whythereisairsurroundingus

　　D．whythereisairpressure

　　2．Airmovesundersuchconditionsthat________.

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　　A．thereisairpressure

　　B．theairisheavy

　　C．airpressuredoesn'tremainthesameallthetime

　　D．aircomesupanddown

　　3．Accordingtothepassageinsameareasiffarmerswhogrowgrapes(葡萄)lightfiresintheearlymorningthatisbecausethefarmerswantto________.

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　　A．driveawaywarmair

　　B．preventcoldairfromcomingtoharmtheirplants

　　C．causemorewind

　　D．stopwarmairrunningaway