人教版八年级英语下册测试卷Unit 4 The Wonders of Nature

Unit4TheWondersofNature

SectionA(la——Id)

基地夯实

I根据句意和首字母提示写出所缺单词

1.XuankongTempleisoneofChina'sw.

2.AnadultSiberiantigerrequiresupto10()skilometersofforesttolivein.

3.Thelakeisfrozenhere.Iguessthetemperaturemustbebzero.

4.Thetopofthemountainisthreekilometersabovesea1.

5.Thesoftheearthwascoveredbywaterbillionsofyearsago.

6.Thehigh-speedrailwaycLuzhouwithChongqingwascompletedinSeptember2024.

H用括号内所给单词的适当形式填空

7.Nowadays,greatinventionsmakeourlivesbetterin(amaze)ways.

8.Humanbeingsshouldgetalongwellwith(natural).

9.Amongallthecinemas,MovieWorldsellstheticketsatthe(low)price.

10TheCaspianSeaisthe(large)ofallthesaltlakes.

HI根据汉语意思完成句子，每空一词

11这个湖有多深？

isthelake?

12请尽可能快地完成作业！

Pleasefinishyourhomeworkyoucan!

13地球上最深的点是哪里？

Where'soncanh?

能力提升

IV.补全对话

根据下面对话中的情境，在每个空白处填入一个适当的语句，使对话恢复完整。

[Andy(A)isanexchangestudentfromtheUK.HeandBinbin(B)areintheNatureClub.]A:Hi,Binbin.I

'mgoingtodoaprojectabouttheQinlingMountains.14.?

B:Sure.Whatdoyouwanttoknow?

A:Letmesee.15.?

B:They'reinShaanxi,thecenterofChina.Themountainsaremorethank600kilometerslong,runni

ngfromeasttowestanddividingnerthemandsouthernChina.Theyhaveaheightof1,200metersonaver

ageabovesealevel.ThehighestmountainisMountTaibai.

A:16.?

B:It'smorethan3,700metershigh.

A:Iguess(heremustbemanyanimalsintheQinlingMountains.Arethereanyvaluableanimals?

B:I7..Manyvaluableanimalslivethere,suchaspandasandgoldenmonkeys.They

arehemetowildlife.

A:Isee.18.

B:Iquiteagreewithyou.That'swhymanypeoplesaytheQinlingMountainsarethelungs省市)ofShaanxiP

rovince.Sowehaveworkedalottoprotectthegreenmountains.

Unit4TheWondersofNature

SectionA(2a—3d)

基础夯实

I.根据句意和首字母提示写出所缺单词

l.Thechildrendidalotofrinthelabtofinishthescienceproject.

2.WhenLiBaienjoyedthew,hesaid,“Itstorrentdashesdownthreethousandfeetfromhigh;

AsiftheSilverRiverfellfromthebluesky.”

3.ThepoolwassodeepthatIcouldnottouchthebofit.

4.Itisnoteasytofindwaterorgreenplantsinad.

n.用括号内所给单词的适当形式填空

5.Witha(deep)of64metres.LakeErieistheshallowestoftheGreatLakes.

6.Jimhasgonetobed?Thisisvery(usual).Healwaysstaysuplate.

7.ZebrafisharctakentoShenzhou-18becausetheyhaveadvantageslikesmallsizeandashort

_(develop)cycle.

8.Doyouknowthe(long)oftheHuangpuRiver?

m.根据汉语意思完成句子，每空一词

9.这艘科研船比许多其他船只下潜得更深。

Thisresearchdeeperthan

10地壳的不同部分承载着山脉和海洋。

Differentoftheearth'scrustmountainsandoceans.

11两河流域和印度河都孕育了早期文明。

MesopotamiatheIndusRiversupportedearly.

12我们必须尽一切办法减少塑料污染。

Wemustreduceplasticpollution.

能力提升

IV.完形填空

Thesealooksverybeautifulwhenthesunisshining(照耀)onit.Butitcanbeveiyterriblewhentherei

sa13wind.Theseaisverybig.It14almostthreequartersoftheearth.Theseaisalsoverydeep(深的)

insonicplaccs.Thcrcisoneplaceandatthatplacetheseaisabout11kilometersdeep.The15mountainint

hewordisabout9kilometershigh.Ifthatmountainwasputintothe16atthatplace.therewouldstillhetw

o17ofwateraboveit!

Inmostpartsofthesea,therearemanykindsof18andplants.Somelivenearthetopofthesea.19

livedeepdown.Thereare20alotofsmalllivingthings,andlotsoffisheslive21them.Theseacanbe

verycold.Whenpeoplegodown,thesea22colderandcolder.Onlysomemencangodownintothedeeps

ea.Butin1970,fivewomenscientistslivedin(hedeepseaforfourteendays.

13.A.strongB.smallC.heavyD.little

14A.addsB.coversC.breaksD.fills

15.A.shortestB.highest

C.farthestD.longest

16.A.riverB.earthC.skyD.sea

17.A.mileB.miles

C.kilometerD.kilometers

18A.fruitsB.potatoes

C.fishesD.vegetables

19A.OtherB.Another

C.OthersD.Theother

20A.tooB.alsoC.againD.yet

21A.inB.forC.onD.at

22.A.becomesB.looks

C.soundsD.seems

V.阅读理解

Ariverisaflowing的)streamofwater.Usually,ariverfeedswaterintoanocean,alake,apond,or

evenanotherriver.Riverscandifferinsizeandthereisnostrictruleonhowbigaflowofwatermustbeto

becalledariver.Herearethefivelongestriversintheworld.

4,132mileslong.Itislocated

inthecontinentofAfrica,

mostlyinthecountriesofEgyptandSudan.ItflowsnorthintotheMediterraneanSea.

TheAmazonRiver

TheAmazonRiverisabout

4,000mileslong.Itislocatedin

thecontinentofSouthAmerica

andflowsthroughseveralcountriesincludingBrazil,Venezuela,Bolivia,andEcuador.ItendsattheAtlantic

Ocean.

TheYangtzeRiver

LocatedinChina,theYangtzeRiverisabout3,915inileslongandflowsintotheEastChinaSea.

TheMississippiRiverandtheMissouriRiver

Theriversystemofthe

MississippiRiverandthe

MissouriRiveristhelongest

riversysteminNorthAmericaat3,709miles.ItflowssouthintotheGulfofMexico.

TheYeniseiRiver

TheYeniseiRiverstarts

inMongoliaandflowsthroughRussiato(heKaraSeaintheArcticOcean.It's3,445mileslong.

Thereare76riversintheworldover1,000mileslong.Alolofpeoplethinkthatriversalwaysflowsouth,

but4ofthe10longestriversintheworldflownorth.TheUnitedStatesalonehasaround3.5millionmilesof

rivers.Fourofthetop10longestriversflowthroughChinaatsomepoint.

23.Whichisthesecondlongestriverintheworld?

A.TheNileRiver.

B.TheMississippiRiver.

C.TheYangtzeRiver.

D.TheAmazonRiver.

24Howmanyriversaretherein(heworldover1,000mileslong?

A.10.B.76.C.4.D.35.

25.WhichofthefollowingisTRUEaccordingtothefactsabove?

A.Ariveralwaysfeedswaterintoanocean.

B.AlltheriversflowthroughChinaatsomepoint.

C.TheMississippiRiverendsattheGulfofMexico.

D.TheNileRiveris155mileslongerthantheYangtzeRiver.

Unit4TheWondersofNature

SectionAGrammarFocus

基枇夯实

I.写出或拼出数字

1.MountQomolangmaisabout(eightthousand,eighthundredandforty-eight)metreshig

h.

2.TheMekongRiverisabout(fourthousand,eighthundredandeighty)kilometreslong.

3.TheGreatBarrierReef(大堡礁)coversanareaof(threehundredandforty-fivethous

and)squarekilometres.

4.TheSaharaDesertcoversanareaofabout9.000,000()squarekilometres.

5.Theaveraged印thofthePacificOceanisabout4,280(Lmetres.

II用括号内所给单词的适当形式填空

6.MyhomeistheclosesttoschoolwhileJim'sisthe(far).

7.AItechnologyinChinahasdeveloped(fast)thananyoneexpected.

8.Doyouthinkwhatthe(deep)seaintheworldis?

9.Actionsspeak(loud)thanwords.

10Someblindanimalscan“see"as(good)asothers.

能力提升

W语法选择

通读下面短文，根据语法和上下文连贯的要求,从每题所给的三个选项中选出一个最佳答案。

Chinaisagreatcountrywithover5,0(X)ycarsofhistory.Therearcmanyplacesofinterestwhichattract11

_touristsfromallovertheworldeveryyear.Someofthemarefantasticlakes,beautifulmountainsandlongriv

ers.

Manymountains,suchasMountTai,MountEmeiandMountHua.areveryfamous.PeoplegotoMountTai

12thesunrise.

13therivers,theYangtzeRiveristhelongestoneandthe14oneistheYellowRiver.Theyarethebir

thplaccsofChineseculture.

Haveyouheardof15lovestoryaboutXuXianandtheWhiteSnake?Itissaidthatthestoryhappened

ontheWestLake.TheWestLakeisoneofthe16placesthatIhaveevervisited.Itis17inHangzhou,

ZhejiangProvince.Manytouristattractionstherearewellworthvisiting,suchasSuCauseway,theBrokenBridg

eandLeiiengPagoda.Thesceneryissoattractivethatvisitorsoftenlose18init.

TheWestLakehasbecome19itsspecialsceneryaswellassomebeautifulpoems.Thesepoemswerewr

ittenbyBaiJuyiandSuDongpo.Besides,thesurroundingareaoftheWestLakeisthehomeofthefamousDra

gonWellTea.

-HaveyoueverbeentotheWestLake?Ifnot,look20achancetogotothewonderfulplace!

11A.millionsofB.millionof

c.threemillions

12.A.sawB.toseeC.seeing

13.A.BetweenB.Among

C.In

14A.twoB.twiceC.second

15.A.aB.anC.the

lbA.fantasticB.rrostfantastic

C.morefantastic

17.A.locatedB.locate

C.location

18A.theirB.them

C.themselves

19A.famousforB.famousas

C.knowas

20A.atB.forC.up

Unit4TheWondersofNature

SectionB(la—le)

基础夯实

I.根据句意和首字母提示写出所缺单词

1.Thelittleplantmanagedtosinthehardenvironment.

2.Insomecountrieschildrenmusttravellongdtoschooleachday.

3.Itisthehighestrailwayintheworldclimbingmorethan5.000metersasealevel.

4.It'simportanttostandupstra：ghtandputyoursback.

5.Tomorrow'stemperatureisbetweentenandfifteend.

6.Thisjobisdangerous,butsomeonehastorhislifetofinishit.

7.Forfurtherinformationontomorrow'sweatherc,callthehotlinebelow.

IL用括号内所给单词的适当形式填空

8.Finally,those(climb)succeededinreachingthetopofthemountain.

9.Theweatherhereis(change),withsuddenstorms.

10Manygiantpandasliveinthemountainsof(north)SichuanProvince.

11Thepink,purpleorwhiteflowersareasignalthattheplantsarenearing(die).

12.Hefindsitimportanttolearnhowtocommunicatewithhis(team).

13Shenzhou-18was(success)launched(发射)intospaceonApril25th,2024.

14.Childrenshow(curious)abouteverything.

15.Thereweremanyfamous(explore)intheworldinhistory.

16Spendingtoomuchtimewatchinggameshowsis(simple)awasteoftime.

HI.根据汉语意思完成句子，每空一词

17渐渐地，太阳从海平面上升起，照亮了整个海滩。

,thesunroseabovethesealevelandlitupthewholebeach.

18这部纪录片向我们展现了人类探索宇宙的雄心。

Thedocumentaryshowsustoexploretheuniverse.

能力提升

IV.完形填空

HaveyoueverheardofMountK2(乔戈里峰)？ItisknownasiheSavageMountainbecausemanypeople

usedtodieorgethurtwhile19it.

K2isthesecondhighestmountainin(heworldafterMountQomolangma.PeoplehardlyclimbMount

K2in20Bothstormsandcoldweathermakeit21toclimbthismountainduringthattime.K2is

famousasoneofthemost22mountainstoclimb.Itisknownbydifferent23suchasCh

ogori,DapsangandMountGodwinAusten.ThenameChogori24"thekingofmountains”.This

mountainliesontheborder(边界)betweenPakistanandChina.

ApartofthemountainliesinPakistan.Theother25ofthemountainliesinXinjiang,China.Thoma

sMontgomeriedidthefirstsurveyofMountK2.Henamedthe26K2.Itwasthesecondpeakmeasur

edintheKarakoramRange,so(hename27thenumber“2”.ThebesttimetoclimbMountK2isbetweenMa

yandSeptember.It28about2weekstocompletetheclimbing.

19A.climbingB.walking

C.swimmingD.moving

20.A.springB.summer

C.autumnD.winter

21A.importantB.impossible

C.silentD.amazing

22.A.difficultB.easy

C.interestingD.sleepy

23.A.namesB.places

C.mountainsD.trees

24.A.listensB.shows

C.callsD.means

25.A.sideB.part

C.joyD.nature

26A.mountainB.people

C.riverD.protection

27.A.completedB.included

C.providedD.depended

28A.spendsB.joins

C.takesD.goes

V.阅读理解

©Oneoftheworld'smostdangeroussportsismountainclimbing,andoneofthemostpopularplacesforth

isistheHimalayas.TheHimalayasrunalongthesouthwesternpartofChina.Ofallthemountains,Qomolangma

risesthehighestandisthemostfamous.Itis8,848.86metershighandisverydangeroustoclimb.Thickclou

dscoverthetopandsnowcanfall\eryhard.Evenmoreseriousdifficultiesincludefreezingweatherconditions

andheavystorms.Itisalsoveryhardtotakeinairasyougetnearthelop.

②ThefirstpeopletoreachthelopwereTenzingNorgayandEdmundHillaryonMay29,1953.Afteralong

anddifficultclimb,troubledbyheavysnow,freezingwindandthelackofoxygen,theyfinallyreachedthetop.

Theycouldonlyspendaboutfifteenminutesonthesummitbeforetheyhadtocomedown.ThefirstChineset

earndidsoin1960.whilethefirstwomantosucceedwasJunkoTabeifromJapanin1975.

③Whydosomanyclimbersrisktheirlives?Oneofthemainreasonsisthatpeoplewanttochallengethems

elvesinthefaceofdifficulties.Thespiritoftheseclimbersshowsusthatweshouldnevergiveuptryingtoachi

eveourdreams.ltalsoshowsthathumanscansometimesbestrongerthantheforcesofnature.

29.HowhighisMountQomolangma?

A.8,848.86kilometers.

B.8.886.48meters.

C.8.848.86meters.

30Accordingtothepassage,whenclimbingMountQomolangma,whatdifficultiesmayclimbersmeet?

A.Thincloudsandheavystorms.

B.Freezingweatherandthickclouds.

C.Heavystormsandlackofwater.

31WhatdoestheunderlinedwordttsummiC,inParagraph2mean?

A.topB.sideC.foot

32Matcheachparagraphwiththemainideas.WhichofthefollowingisTRUE?

A.①-Spiritofclimbers;®-Achievementsofclimbers;③-Factsanddangers

B.©-Achievementsofclimbers;②-Factsanddangers;③-Spiritofclimbers

C.①-Factsanddangers;②-Achievementsofclimbers;③-Spiritofclimbers

33.Whatdoesthespiritofclimberstellus?

A.Nevergiveup.

B.AllroadsleadtoRome.

C.Practicemakesperfect.

Unit4TheWondersofNature

SectionB(2a-Project)

取出夯实

1根据句意和首字母提示写出所缺单词

1.Look,childrenarebuildingcastles(城堡)withson(hebeach.They'rehavingfun.

2.Edisonhadmorethanonethousandinventionsduringhis1.

3.Plantingsomeflowersinyourgardenisveryhelpfulforabees.

4.Nice(尼斯)liesonFrance'ssoutheastc.Itswonderfulbeachesaretheperfectplacesf

orsummerholidays.

5.Ihaveasmallhouse.Itiabedroom,akitchenandabathroom.

6.Newtofenergyfromthesun,windandwaterproducelittlepollutionandwillneverrunout.

II.用括号内所给单词的适当形式填空

7.Thesignsaystheareais(risk),soweshouldn'tgothere.

8.Lotsoftouristsfromthe(south)partofChinahavebeentoHarbintwice.

9.As(travel),wcshouldrememberthatwheninRome,doasRomansdo.

10.ManyvisitorscometoXizangeveryyearbecauseofits(nature)environinent.

11.Cleanwaterisimportanttokeepfish(live)inthelake.

12.Myhometownliesinthe(northeast)partofourcountry.

13Theclassmatesbecamevery(curiosity)aboutthetangram(七巧板)andwantedtohaveat

14Ourcampis(location)intheSwissAlps.

15Theytookpartinvariousactivitiesthisterm,(include)plantingcropsandcoo

kingmeals.

能力提升

in阅读还原

自然景观「2024陕西中考」

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

Rainforestsareforests(hatgetalotofrain.Itcanrainmorethanoneinch(=2.54cm)perday!Therearetro

pical(热带的)rainforestsallovertheworld.16Theyareverywarm.

TheAmazonisinSouthAmerica.Itisthebiggestrainforestintheworld.Morethanhalfcftherainforesti

sinBrazil.17

ManyplantsandanimalsliveintheAmazon.Therearemorekindsofplantsandanimalstherethananywher

eelseintheworld.Thebiggestmixofplantsandanimalslivesinthecanopy.18Thecanopykeepsoffm

ostofthesunlight.Therainforestfloorisverydark.

19Therearemorethan400differentnativetribes（土著部落）！Nativepeopleusedtostayintherainforest.

Theyfoundfoodandbuilthomes（here.Theymademedicinefromplants.Nowtheysometimesleave.Theygo

tonearbytownstosellfood.Still,theyliveintheirownways.

Today,theAmazonisfacedwiththeproblemofdeforestation.Thismeansthattoomany

treesarccutdownbyhumansand20

Whatcanwedotoprotecttherainforestandthewildlifethere?

AThecanopyisathickcoatoftrees.

B.Theyarefoundneartheequator（赤道）.

C.itbringsharmfulresultstothewildlifeintheAmazon.

DitmakesmorespacefortheanimalsintheAmazontolivein.

E.Theyhavefoundsomewildlifeneartheequator.

F.Therestspreadsacrosseightothercountries.

G.PeopleliveintheAmazontoo.

16.17.18.19.20.

M任务型阅读

阅读下文并回答问题。

Dearfriends,

Lastmonth,westartedtheuNatureandMe'activity.Whatdidyouseeanddoduringyourtimewithnature?

Andhewdidyoufeel?Pleaseshareyourstories.

8:15p.m.31May

SteveIdislikedhikinginthepast,bu（nowIenjoyit.MyfatherandIhadahikingtripontheMacLehose

TrailinHongKong.ThejourneywasharderthanIexpected.Mylegsstartedburningafterjust30minutes.B

utasweclimbedhigher,theamazingviews------greenhills,goldenbeaches,andendlessocean------seemed

undermyfeet.There'sanoldChinesesaying,“Whenyouclimbtothetop,allothermounUinsseemsmall/5

That'sexactlyhowIfelt.Everydropofsweatcounts!

Replyhere.

8:17p.m.31May

Lan“Ifeelfreeandpeaceful.MThiswasmyanswertomyfriendwhensheaskedmehowIfeltaftera

nafternoonwalk.Aswewalkedthrough（hepark,Inoticedallthosefallenleaveswithdifferentshapesan

dcolorslyingontheground.Ipickedsomeupandmadethemintoapicture.

Ycuknowwhattheysay,“Thebestthinginlifeisfrec.^^That'ssotrue.Bywalking,Igotgoodexercise.B

ycollectingtheselittletreasures,!startedpayingattentiontoallthesmallthingsaroundmethatIusedtom

iss.Itwaslikeanescape（逃离）fromwhatwastroublingme.

R叩lyhere.

12minutesago

JanetDuringtheholiday,myfamilyandIwenttoCrystalWaterfalls.Itwasamazing!Istoodnear（hefall

s.hearingtherushofwaterandfeeling（hecoolmist（水雾）.Thesoundofthewalerwasactuallysuperre

laxing.Itfeltlikeallmytirednessandworrieswerebeingwashedaway.

Backhome.Ievendownloadediherecordingsofwaterfallsonline.Theycanhelpmesleepbetter!

Replyhere.

21DoesStevelikehikingnow?

22.WhatdidLanpickupduringtheafternoonwalk?

23.Whathavethethreepeoplelearnedincommonfromtheirtrips?

24Whatdoyouthinkoftheirexperiencesandwhy?Chooseonetoreply.（about30words）

Unit4TheWondersofNature自主检测

I完形填空（每小题1分，共15分）

Cloudsoftenappearinthe1,butdoyoureallystopto_2_atthem?Doyouwonderabouttheirnames?

Theactivityiscalledcloudspotting（观云）.

JiYun,bornin1987,isacloudspotterinBeijing.Heenjoys3aboutthem,suchasknowingtheirnames

accordinatotheir4

Jiloves5deeply.Hebegantofindoutmoreaboutthebeautyofcloudsaftertakingsomephotosofani

cehalo（冰晕）."Ican'tstopmyselffrom6ihem,“saidJi.

InOctober2013,Jigota（n）7fromafriend.Therewerevery_8_asperitasclouds（糙面云）inBeijing,an

dtheywerequicklygoingsoutheast.“9Igottheinformation,Irushedoutofmyhome,“Jisaid.10aseco

ndthought,helookahigh-speedtrainloTianjin.Althattime,thetrainsweren'tasIIastoday's.In（heend,

he12tookphotosofthecloudsinTianjin'sWuqingarea.Thecloudwasoneoftheworld's1310rarest

（罕见的）clouds.

Ji'sstorymade14popular.Aroundthattime,hecreatedsomeonlinegroupsto15thesameloveforcl

oudswithfans.Hesaid,“Canacloudoraneveningskymakeyoustopandlookup?Ifyes,pleasejoinus.”

1.A.landB.skyC.oceanD.desert

2.A.lookintoB.lookfor

C.lookupD.lookdown

3.A.learningB.bringing

C.talkingD.worrying

4.A.seasonsB.time

C.sizesD.shapes

5.A.natureB.music

C.sportD.art

6.A.feelingB.discussing

C.researchingD.seeing

7.A.noticeB.advice

C.opinionD.message

8.A.darkB.special

C.normalD.terrible

9.A.BeforeB.Until

C.UnlessD.Assoonas

10A.WithB.Without

C.AtD.In

11A.bigB.long

C.fewD.conimon

12.A.quicklyB.successfully

C.carefullyD.easily

13.A.famousB.beautiful

C.topD.nice

14A.himB.herC.youD.them

15.A.sendB.tellC.writeD.share

n阅读理解（每小题2分，共16分）

TheAmazonisoneoftheworld'slongestrivers,secondonlytotheNileinAfrica.Beginningfromt

heAndesMountainsinPeru,theAmazonruns4,000mileseastwardthroughColombiaandBraziltoiheAll

anticOcean.Theriverisusuallyaboutonetosixmileswide.Duringtherainyseason,itcanbeasmuchas20m

ileswideinsomeareas.Itisalsooreofthedeepestrivers,reaching300feetdeepinanumberofareas.

TheriverisalsoimportantbecauseitrunsthroughtheAmazonrainforest.Hometosomecftheplanet'sm

ostamazingandunusualbirds,fish,insects,andanimals,theAmazonrainforesthasthemostplantandanimals

pccies（物种）intheworld.Brightlycoloredparrots,monkeys,andfrogslivehere.Inthewater,you'11findpin

kdolphins.Someoftheplantsandtreesintherainforesthavebeenusedasmedicinesforthousandsofyears.

TheriverbecameknownastheAmazonduringthemid-1500s.ASpanishman（西班牙人）sawsonicwome

nfightersalongitslowerbanksandnamedtheriverafterthem.InGreekmythology（神话），theAmazonswere

agroupofwomenwhowereverygoodatfighting.

16WhichcountrydoestheAmazonrunthrough?

A.Brazil.B.India.

C.SouthAfrica.D.France.

17Whatdoes''AmazorTmeanaccordingtothelastparagraph?

A.ASpanishman.B.Alongriver.

C.Arainforest.D.Awomanfighter.

18.Whatcanbethebesttitleforthepassage?

A.TheAmazon

B.TheAmazonRainForest

C.TheAnimalsin（heAmazon

D.TheStoryabouttheAmazon

B

Ablueholeisafloodedseacave（洞穴）withaholethatopensupattheland'ssurface.Thesecavesystems

formincarbonaterock,oftenonislands.FarbelowsealeveltherearesomeofthehardestenvironmentsonEar

th,wi:hnooxygen（氧）andnolight.Yettheseareasarefilledwithlifeformsthathavegotusedtosuchcon

dilions.

Blueholesgettheirnamefrom（hecolorthatsomehavewhenseenfromtheair.Itisusua'lyareflectiono

ftheskyonthewater.★Somehavedarkormuddywater.

Blueholeshaveseverallayersofwater,chemicalsandbacteria（细菌）.Thetoplayeroffreshwatercomesfr

omrainfall,whichactslikeacapontopofthelayeredmixtureandkeepsoutoxygenfromtheair.Thefreshw

atcrcoversadenserlayerofsaltwater.Underneaththisisalayerofpoisonoushydrogensulfide（有毒的硫化氢）,

producedbybacterialivinginthewater.Atthebottomisanoxicseawater—waterthatdoesnothaveanyoxyg

cn.

“Underwatercavesareprobablyoneoftheleastunderstoodecosystemsontheplanet,nKennyBroad,as

cientistattheUniversityofMiamiinFlorida,says."Onereasonisthatyoustillphysicallyhavetogothere—y

oucan'lsendinasubmarine（潜水艇）oranyothermachine.”

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