Wearenowlivinginthemodernsociety.Mostoftheenergyweuseforheatinglightingtransportationandmanufacturing(制造业)comesfromfossil(化石)fuels.Thesearecarbon-basedfuelsfromoilcoalandnaturalgas.Whenw

　　Wearenowlivinginthemodernsociety.Mostoftheenergyweuseforheatinglightingtransportationandmanufacturing(制造业)comesfromfossil(化石)fuels.Thesearecarbon-basedfuelsfromoilcoalandnaturalgas.Whenweburnthesefuelswereleaseheatwhichp__小题1:___theenergy.

　　Therearethreemaindisadvantagestousingthesefuels.FirstlytheyarecausingclimateproblemsbecauseoftheG_小题2:___Effect.Whenweburnfossilfuelstheyproducecarbondioxidewhichcausesglobalwarming.Secondlywhenwehaveusedupallourcoaloilandnaturalgaswewillhaven__小题3:__lefttoburn.Thirdlytheyarenotveryefficient.Theinternalcombustionengine(内燃机)thatweuseinmostcarstrucksandbusesforexampleisonlyabout14%efficient.

　　Scientistsareworkingonanotherfuel—hydrogen.Thereareacoupleofadvantagestousinghydrogenasafuel.Firstlybecausetwo-thirdsofthee__小题4:__surfaceiswaterandwaterismadeofhydrogenandoxygen.Thereisanalmostunlimitedsupplyofhydrogen.Secondlyburninghydrogendoesnotcauseglobalwarming.Thirdlyitismuchmoreefficientthancarbon-basedfuels.

　　Unfortunatelythereareproblemswithhydrogenatthepresenttime:thereistheproblemofseparating(分离)itfromwaterc_小题5:___andthereisthedifficultyofstoringit.Itcanbestoredunderpressurebuthighpressuretanksarefarfromsafe.Itcanalsobestoredasaliquidbutonlyatextremelylowtemperatures.Itseemslikelythereforethattherewillhavetobeacompletelynewtechnologybeforehydrogenreplacesfossilfuels.S__小题6:___theseproblemsisanurgent(急迫的)matter.AlthoughChinaIndiaandAustraliahavehugeamountsofcheapcoalandtherearestilll__小题7:___oilandgasreserves(储藏量)elsewheretheeffectsontheplanet’sclimatewillbebadiftheyareused.