专四英语听力答案

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1、WavesHowdoeslightgetfromthesuntotheearth?Howdoesmusicgetfromthestagetotheaudience?Theymovethesameway-----inwaves!Lightandsoundarefomp3sofenergy.Allwavescarryenergy,buttheymaycarryitdifferently.Lightandsoundtravelthroughdifferentkindsofmatter.Forexample,lightwavescannotmovethroughwalls,butsoundwave

2、scan.Thatiswhyyoucanhearpeopletalkinginanotherroomeventhoughyoucannotseethem.Theenergyofsomewavesisdestructive.Anearthquakeproducesseismicwaves.Catchawave.Askafriendtostandafewfeetawayfromyou.Stretchaspringbetweenyou.Shakethespringtotransferenergytoit.Whathappens?Thespringbouncesupanddowninwaves.W

3、henthewavesreachyourfriend,theybouncebacktoyou!Lightwavestravel300,000kilometers(186,000miles)persecond!Theycanalsotravelthroughavacuum.Thatiswhylightfromthesunanddistantstarscantravelthroughspacetotheearth!SoilsTherearemanydifferentkindsofsoils.Differentsoilshavedifferenttypesofrockandmineralsint

4、hem.Somesoilshavemorewaterinthemthanothers.Somesoilsmighthavemoreplantandanimalmaterialinthem,too.Differentkindsofsoilsarefoundindifferentpartsoftheworld.ThereareseveralkindsofsoilsfoundintheUnitedStates.Insomeareas,thesoilhasalotofclay.Othersoilsareverysandy.Loamisakindofsoilthathasagoodmixtureof

5、clayandsand.Insomeplaces,soillayersareverythick.Lotsofplantsgrowinplaceswithathicksoillayer.Indryandwindyplacessoillayersaremuchthinner.Layersofsoilonmountainsarethinbecausegravitypullsthesoildownhill.Thetypeofsoilinaparticularplaceaffectswhatkindsofplantscangrowthere.CrisisLifeisacontest!Whowillw

6、in?Abluebirdandsparrowbothcompeteforspacetobuildtheirnests.Afast-growingmapletreeandslower-growingdogwoodcompeteforthesunlighttheybothneed.Oilcompeteswithcoalandnuclearpowerasanenergysourceforelectricpowerplants!Thereisaproblem.Thereisalimitedamountofspaceforbirds,sunlightfortrees,andenergyforpeop

7、le!Ifwedonotcutbackonourusesofsomeofourresources,somedaytheywillbegone!Howcanweuseenergytodayandknowwewillhaveenoughtogoaroundinthefuture?Wecanchoosealternate,orreplacement,energyresources.Ittakestheearthmillions