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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、10
B、20
C、30
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正确答案:

C

答案解析:

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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.

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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.

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