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1、1994Passage4 "Ihavegreatconfidencethatbytheendofthedecadewe'llknowinvastdetailhowcancercellsarise,"saysmicrobiologistRobertWeinberg,anexpertoncancer."But,"hecautions,"somepeoplemayhavetheideathatonceoneunderstandsthecauses,thecurewillrapidlyfollow.ConsiderPas
2、teur.Hediscoveredthecausesofmanykindsofinfections,butitwasfiftyorsixtyyearsbeforecureswereavailable." Thisyear,50percentofthe910000peoplewhosufferfromcancerwillsurviveatleastfiveyears.Intheyear2000,theNationalCancerInstituteestimates,thatfigurewillbe75percent
3、.Forsomeskincancers,thefive-yearsurvivalrateisashighas90percent.Butothersurvivalstatisticsarestilldiscouraging—13percentforlungcancer,and2percentforcancerofthepancreas. Withasmanyas120varietiesinexistence,discoveringhowcancerworksisnoteasy.Theresearchersmadeg
4、reatprogressintheearly1970s,whentheydiscoveredthatoncogenes,whicharecancer-causinggenes,areinactiveinnormalcells.Anythingfromcosmicraystoradiationtodietmayactivateadormantoncogene,buthowremainsunknown.Ifseveraloncogenesaredrivenintoaction,thecell,unabletoturnt
5、hemoff,becomescancerous. Theexactmechanismsinvolvedarestillmysterious,butthelikelihoodthatmanycancersareinitiatedatthelevelofgenessuggeststhatwewillneverpreventallcancers."Changesareanormalpartoftheevolutionaryprocess,"saysoncologistWilliamHayward.Environment
6、alfactorscanneverbetotallyeliminated;asHaywardpointsout,"Wecan'tprepareamedicineagainstcosmicrays." Theprospectsforcure,thoughstilldistant,arebrighter. "First,weneedtounderstandhowthenormalcellcontrolsitself.Second,wehavetodeterminewhethertherearealimitednum
7、berofgenesincellswhicharealwaysresponsibleforatleastpartofthetrouble.Ifwecanunderstandhowcancerworks,wecancounteractitsaction."63.TheexampleofPasteurinthepassageisusedto________. [A]predictthatthesecretofcancerwillbedisclosedinadecade [B]indicatethattheprosp
8、ectsforcuringcancerarebright [C]provethatcancerwillbecuredinfiftytosixtyyears [D]warnthatthereisstillalongwaytogobeforecancercanbeconquered64.Theauthorimpliesthatbytheyear2000,__
