【GRE里一道逻辑题,请赐教!Editorial:Criticsofnuclearpowercomplainabouttheallegedlyseriousharmthatmightresultfromcontinuedoperationofexistingnuclearpowerplants.Butsuchconcernsdonotjustifyclosingtheseplants;afterall】

　　GRE里一道逻辑题,请赐教!

　　Editorial:

　　Criticsofnuclearpowercomplainabouttheallegedlyseriousharmthatmightresultfromcontinuedoperationofexistingnuclearpowerplants.Butsuchconcernsdonotjustifyclosingtheseplants;afterall,theiroperationhascausednomoreharmthanthatcausedbypollutiongeneratedbycoal-andoil-burningpowerplants,themostimportantothersourcesofenergy.

　　Whichofthefollowingisanassumptiononwhichtheargumentdepends?

　　(A)Existingnuclearpowerplantsshouldbeclosedonlyifitcanbeconclusivelydemonstratedthattheircontinuedoperationislikelytocauseharmmoreseriousthantheharmtheiroperationhasalreadycaused.

　　(B)Closingexistingnuclearpowerplantswouldrequiregreatlyincreasedrelianceoncoal-andoil-burningpowerplants.

　　(C)Theharmthathasresultedfromoperationofexistingcoal-andoil-burningpowerplantshasbeensignificant.

　　(D)Theharmthatanuclearpowerplantislikelytocauseasitcontinuestooperatecanbereliablypredictedfromthepasthistoryofnuclearpowerplants.

　　(E)Theonlyharmthathasresultedfromoperationofexistingcoal-andoil-burningpowerplantshasresultedfromthepollutiongeneratedbytheseplants.

　　答案是D,我真心没明白...