【SeenfromspacetheEarthiscoveredinabluemantle.Itisaplanetonwhichthecontinentsaredwarfed(相形见绌)bytheoceanssurroundingthemandthevastnessofthemarinearea.Anastonishing80percentofallthelifeonE】
SeenfromspacetheEarthiscoveredinabluemantle.Itisaplanetonwhichthecontinentsaredwarfed(相形见绌)bytheoceanssurroundingthemandthevastnessofthemarinearea.
Anastonishing80percentofallthelifeonEarthistobefoundhiddenbeneaththewavesandthisvastglobaloceanpulsesaroundourworlddrivingthenaturalforceswhichkeeplifeonourplanet.
TheoceansprovidenecessarysourcesofproteinenergymineralsandotherproductsofusetheworldoverandtherollingoftheseaacrosstheplanetcreatesoverhalfouroxygendrivesweathersystemsandnaturalflowsofenergyandnutrientsaroundtheworldtransportswatermassesmanytimesgreaterthanalltheriversonlandcombinedandkeepstheEarthhabitable.
WithouttheglobaloceantherewouldbenolifeonEarth.
Itisseriouslyworryingthenthatwearedamagingtheoceansonascalethatisunimaginabletomostpeople.
Wenowknowthathumanactivitycanhaveseriousinfluencesonthevitalforcesgoverningourplanet.Wehavefundamentallychangedourglobalclimateandarejustbeginningtounderstandtheconsequencesofthat.Asyetlargelyunseen，butjustasserious，aretheinfluenceswearehavingontheoceans.Ahealthyoceanhasdiverseecosystemsandstrongandhealthyhabitats.Theactualstateofouroceansisafarcryfromthisnaturallevel.
Alargequantityofhumanpressuresarebeingexertedbothdirectlyandindirectlyonoceanecosystemstheworldover.Consequentlyecosystemsarecollapsingasmarinespeciesaredriventowardsextinctionandoceanhabitatsaredestroyed.Withthedecreaseandremovementoftheirdiversityoceanecosystemsarelosingtheirnaturalrecovery.
20．The2ndandthe3rdparagraphsaregivenmainlytodescribe________．
A．whattheoceanslooklike
B．whattheoceansaremadeupof
C．whatlivesintheoceans
D．whatfunctionstheoceanshave
21．Theoceansprovideallthefollowingexcept________．
A.variousmarinecreatures
B.richlivingresources
C.allnaturalforces
D.comfortablehabitatsforman
22．Manhasnotyetrealizedthat________．
A．hehasdoneharmtotheoceans
B．hehasdoneharmtothepl