Coralreefs（珊瑚礁）arenotjustbeautifultolookat，butalsoveryuseful．Theyshelternearly
25% ofoceanlifeandprovidefoodforbillionsofpeople．However，likemanyotherspecies，thisamazingecosystem（生态系统）isindangerofdyingout!
Therearetwomainreasonsforthedestruction-therisingcarbondioxidelevelscausedbyglobalwarmingaswellashumaninfluenceslikebottomoperation．Whilenotmuchcanbedoneabouttheformer，thelosscausedbythelattercanbereduced．
Bottomoperationinvolvesdroppingnetstotheoceanbedandthendraggingthemupwhenfilledwithfish．Thisactiondamagedtheoceanfloor，causingthecoralbranchestoseparatefromthereefs．Whilethatisverydiscouraging，thegoodnewsisthatifthesebranchesarefoundquickly，theycanbesaved．Atpresent，thatworkisbeingperformedbyvolunteerdivers．Butthemethodhasonlylimitedsuccessbecausetheycannotstaylongunderwater，norreachdepthsofover200meterswheresomeofthedeep-seacoralgrows．
However，thisisnotthecaseforCoralbots-therobotsthatcanconstantlyseekoutbrokenbranches．Ateamof‘coralbots'，eachindividuallyworkingtosimpleruleswillpiecetogetherdamagedbitsofcoral，allowingthemtoregrow．Theyareprogrammedtobeabletodistinguishbetweenotherthingsandthecoral．Therobotsworktogetheringroups，similartobees．Ifonecoralbotisdamagedthentheotherswillstillbeabletocompletethetask．
DrLea-AnneHenrysaid："Theprojectofusingcoralbotsoffersusthepossibilitytorestore（修复）thefunctionofreefs．Itisinthefinalstageoftesting．Onceready，theresearchershopetobuildhundredsofthemandusethemeffectivelyinthewatersoffScotlandandthenhopefullyintheoceansacrosstheworld．"
32．Whichofthefollowingisacauseofthedangerthatcoralreefsarefacing？___
A．Theappearanceofnewcreatures．
B．Theseriouslypollutedseawater．
C．Theactivitiesofvolunteerdivers．
D．Humanactivitieslikebottomoperation．
33．Comparedwithvolunteerdivers，coralbots___．
A．canstaylongerunderwater B．mustworkasbeesdo
C．candistinguishwhatiscoral D．canneverbedamaged
34．Whatdoest