Somescientistssaythatanimalsintheoceanareincreasinglythreatenedbynoisepollutioncausedbyhumanbeings.Thenoisethataffectseacreaturescomesfromanumberofhumanactivities.Itiscausedmainlybyindustrialunderwaterexplosions,oceandrilling,andshipengines.Suchnoisesareaddedtonaturalsounds.Thesesoundsincludethebreakingoficefields,underwaterearthquakes,andsoundsmadebyanimalsthemselves.
Decibels（分贝）measuredinwateraredifferentfromthosemeasuredonland.Anoiseofonehundredandtwentydecibelsonlandcausespaintohumanears.Inwater,adecibellevelofonehundredandninety-fivewouldhavethesameeffect.
Somescientistshaveproposedsettinganoiselimitofonehundredandtwentydecibelsinoceans.Theyhaveobservedthatnoisesatthatlevelcanfrightenandconfusewhales.
AteamofAmericanandCanadianscientistsdiscoveredthatloudnoisescanseriouslyinjuresomeanimals.Theresearchteamfoundthatpowerfulunderwaterexplosionswerecausingwhalesintheareatolosetheirhearing.Thisseriouslyaffectedthewhales’abilitytoexchangeinformationandfindtheirway.Someofthewhalesevendied.Theexplosionshadcausedtheirearstobleedandbecomeinfected.
Manyresearcherswhoseworkdependsonoceansoundsobjecttoalimitofonehundredandtwentydecibels.Theysaysuchalimitwouldmeananendtoimportantindustrialandscientificresearch.
Scientistsdonotknowhowmuchandwhatkindsofnoisesareharmfultooceananimals.However,manyscientistssuspectthatnoiseisagreaterdangerthantheybelieved.Theywanttopreventnoisesfromharmingcreaturesintheocean.
小题1:Accordingtothepassage,whichofthefollowingisincreasinglydangeroustoseacreatures?