不宜作为循环空气来使用的有害气体浓度大于职业接触限值的()%时。
A、10C
暂无解析
_____,hecannowonlywatchitonTVathome.
ThediscoveryoftheAntarcticnotonlyprovedoneofthemostinterestingofallgeographicaladventures,butcreatedwhatmightbecalled“theheroicageofAntarcticexploration”.Bytheirtremendousheroism,mensuchasShakleton,Scott,andAmundsencausedanewcontinenttoemergefromtheshadows,andyetthatheroicage,littlemorethanacenturyold,isalreadypassing.Modernscienceandinventionsarerevolutionizingtheendurance,futurejourneysintotheseicywasteswillprobablydependonmotorvehiclesequippedwithcaterpillartractionratherthanonthedogsthatearlierdiscoverersfoundsoinvaluableandhardlycomparable.
FewrealizethatthisAntarcticcontinentisalmostequalinsizetoSouthAmerica,andenormousfieldofworkawaitsgeographersandprospectors.Thecoastsofthiscontinentremaintobeaccuratelycharted,andthemapingofthewholeoftheinteriorpresentsaformidabletasktothecartographerswhoundertakethework.Oncetheirlaborsarecompleted,itwillbepossibletoprospectthevastnaturalresourceswhichscientistsbelievewillfurnishoneofthelargesttreasurehoardsofmetalsandmineralstheworldhasyetknown,andalmostinexhaustiblesourcesofcopper,coal,uranium,andmanyotheroreswillbecomeavailabletoman.SuchdiscoverieswillusherinaneraofpracticalexploitationoftheAntarcticwastes.
Thepolardarknesswhichhidesthiscontinentforthesixwintermonthswillbedefeatedbyhugebatteriesoflight,andmakepossibletheestablishingofair-fieldsforthefutureinter-continentalairservicesbymakingtheseareasaslightasday.Presentflyingrouteswillbecompletelychanged,fortheAntarcticrefuelingbaseswillmakeflightsfromAustraliatoSouthAmericacomparativelyeasyoverthe5,000milesjourney.
Theclimateisnotlikelytoofferaninsuperableproblem,fortheexplorerAdmiralByrdhasshownthattheclimateispossibleevenformencompletelyuntrainedforexpeditionsintothosefrozenwastes.Someofhispartiesweremenwhohadneverseensnowbefore,andyetherecordsthattheysurvivedtherigorsoftheAntarcticclimatecomfortably,sothat,providedthattheappropriateinstallationsaremade,wemayassumethathumanbeingsfromallcountriescouldlivetheresafely.Byrdevenaffirmsthatitisprobablythemosthealthyclimateintheworld,fortheintensecoldofthousandsofyearshassterilizethiscontinent,andrendereditabsolutelygermfree,withtheconsequencesthatordinaryandextraordinarysicknessanddiseasesfromwhichmansuffersinotherzoneswithdifferentclimatesarehereutterlyunknown.Thereexistnoproblemsofconservationandpreservationoffoodsupplies,forthelatterkeepindefinitelywithoutanysignsofdeterioration;itmayevenbethatlatergenerationswillcometoregardtheAntarcticasthenaturalstorehouseforthewholeworld.
Plansarealreadyonfoottosetuppermanentbasesontheshoresofthiscontinent,andwhatsofewyearsagowasregardedasa“deadcontinent”nowpromisestobeamostactivecenterofhumanlifeandendeavor.
1.WhendidmanbegintoexploretheAntarctic?
A.About100yearsago.
B.Inthiscentury.
C.Atthebeginningofthe19thcentury.
D.In1798.
2.Whatmusttheexplorersbe,eventhoughtheyhavemodernequipmentandtechniques?
A.Braveandtough
B.Stubbornandarrogant.
C.Well-likedandhumorous.
D.Stoutandsmart.
3.Themosthealthyclimateintheworldis___.
A.inSouthAmerica.
B.intheArcticRegion.
C.intheAntarcticContinent.
D.intheAtlanticOcean.
4.WhatkindofmetalsandmineralscanwefindintheAntarctic?
A.Magnetite,coalandores.
B.Copper,coalanduranium.
C.Silver,naturalgasanduranium.
D.Aluminum,copperandnaturalgas.
5.Whatisplannedforthecontinent?
A.Buildingdamsalongthecoasts.
B.Settingupseveralsummerresortsalongthecoasts.
C.Mappingthecoastandwholeterritory.
D.Settinguppermanentbasesonthecoasts.
.IfyouhavereallybeenstudyingEnglishforsolong,it’sabouttimeyou_____abletowritelettersinEnglish.
Thematterisnottobe____.
Californiaisalandofvarietyandcontrast.Almosteverytypeofphysicallandfeature,sortofarcticicefieldsandtropicaljunglescanbefoundwithinitsborders.Sharplycontrastingtypesoflandoftenlieveryclosetooneanother.PeoplelivinginBakersfield,forinstance,canvisitthePacificOceanandthecoastalplain,thefertileSanJoaquinValley,thearidMojaveDesert,andthehighSierraNevada,allwithinaradiusofabout100miles.Inotherareasitispossibletogosnowskiinginthemorningandsurfingintheeveningofthesameday,withouthavingtotravellongdistance.ContrastaboundsinCalifornia.ThehighestpointintheUnitedStates(outsideAlaska)isinCalifornia,andsoisthelowestpoint(includingAlaska)。MountWhitney,14,494feetabovesealevel,isseparatedfromDeathValley,282feetbelowsealevel,byadistanceofonly100miles.Thetwoareashaveadifferenceinaltitudeofalmostthreemiles.Californiahasdeep,clearmountainlakeslikeLakeTahoe,thedeepestinthecountry,butitalsohasshallow,saltydesertlakes.IthasLakeTulainyo,12,020feetabovesealevel,andthelowestlakeinthecountry,theSaltonSea,236feetbelowsealevel.Someofitslakes,likeOwensLakeinDeathValley,arenotlakesatall:theyaredrieduplakebeds.Inadditiontomountains,lakes,valleys,deserts,andplateaus,CaliforniahasitsPacificcoastline,stretchinglongerthanthecoastlinesofOregonandWashingtoncombined.
1.WhichofthefollowingisthelowestpointintheUnitedStates?
A.LakeTulainyoB.MojavedesertC.DeathValleyD.TheSaltonSea
2.WhereisthehighestpointintheUnitedStateslocated?
A.LakeTahoe.
B.SierraNevada.C.MountWhitney.
D.Alaska.
3.HowfarawayisDeathValleyfromMountWhitney?
A.About3miles.
D.14,494feet.
4.WhichofthefollowingisNOTmentionedinthepassageasbeingwithinaradiusofabout100milesofBakersfield?
A.ThePacificOcean.
B.SanJoaquinValley.
C.MojaveDesert.
D.OregonandWashington.
5.WhichstatementbestdemonstratesthatCaliforniaisalandofvarietyandcontrast?
A.ThehighestlakeinCaliforniaisLakeTulainyo.
B.ItispossibletogosurfingandsnowskiinginsomepartsofCaliforniawithouthavingtotravellongdistance.
C.SierraNevada,SanJoaquinValley,MojaveDesertandthePacificOceanallliewithinaradiusofabout100miles.
D.OwensLake,inDeathValley,isnotreallyalakeatall.