Duringonesummernotlongago,AmericansintheSouthwestwerewithoutrainformanydays.Thesunburnedupcrops.Animalswenthungryonthedryland.Atlast,cloudsappearedintheskyandsentdownrain.Howdosuchcloudsform?Thesun,theearth,andthe

　　Duringonesummernotlongago,AmericansintheSouthwestwerewithoutrainformanydays.Thesunburnedupcrops.Animalswenthungryonthedryland.Atlast,cloudsappearedintheskyandsentdownrain.

　　Howdosuchcloudsform?Thesun,theearth,andtheairallplayapart.Thechangesthattakeplacebeforecloudscanformdonotalwayshappenquickly.First,theearthisheatedbythesun.Thiscausestinydropsofwaterinoceansandriverstoriseandmixwithair.Asthewetairriseshigher,itcoolsoff,makingclouds.

　　Whatcausesthesecloudstobecomerain?Thetinydropsofwaterinsidethecloudsbecomelargerastheygathermorewetnessfromtheairaroundthem.Finally,thedropsbecomesolargethattheycannolongerbeheldupbytheair.Theyfalltothegroundasrain.

　　Theraindropsthatfallarenotalwaysthesamesize.Somemaybeverylarge.Butthesmallestcomedowninafinemist.

　　Rainisneededforalllife.Whenitfallsafteralongdryspell,trees,grass,andbushesmaybegintolookfreshandgreenagain.Theseplantsneedwatertostayhealthy.Therainalsocausesstreamstofillwithwater.Thismakesitpossibleforfishandotheranimalstolive.Rainbringsnewlifeandhopetomillionsofpeopleandotherlivingthings.

　　1.Thefirstparagraphmentionstheperiodoftimeduringwhichtheweatherwasveryandcropswere.

　　A.rainy,burntB.drought,burntup

　　C.drought,burntD.dry,burntup

　　2.Thephrase“playapart”means.

　　A.bearoleB.formasapart

　　C.connectwitheachotherD.makeacontribution

　　3.Concerninghowraincomesintobeing,whichstatementistrue?

　　A.Alotofdropsofwaterriseandmixwithairasthesunshines.

　　B.Wetaircoolsoffasitriseshigher.

　　C.Thedropsbecomelargerandlargerastheygathermorewetness.

　　D.Thedropsfalltothegroundastheybecometoolargetoholdup.

　　4.Inthelastparagraph,theword“spell”means.

　　A.weatherB.aperiod

　　C.timesD.noneoftheabove

　　5.Thispassagemainlyexplainsofcloudsandrain.

　　A.theformationB.thephenomena

　　C.theimportanceD.thefunction