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1、2019-2020年高考英语二轮复习阅读理解训练（2）(V)请认真阅读下列短文，从短文后各题所给的A、B、C、D四个选项中，选出最佳选项。Fordecades,publichealthofficialshavepuzzledoverasurprisingfactaboutHIV:Onlyabout10-20percentofinfantswhoarebreastfedbyinfectedmotherscatchthevirus.Testsshow,though,thatHIVisindeedpresentinbreastmilk,sothesechildrenareexposedtothevi
2、rusmultipletimesdailyforthefirstseveralmonthsoftheirlives.Now,agroupofscientistsanddoctorsfromDukeUniversityhasfiguredout whythesebabiesdon’tgetinfected.Humanbreastmilknaturallycontainsaproteincalled TenascinC thatneutralizesHIVand,inmostcases,preventsitfrombeingpassedfrommothertochild.Eventually,th
3、eysay,theproteincouldpotentiallybevaluableasanHIV-fightingtoolforbothinfantsandadultsthatareeitherHIV-positiveoratriskofcontractingtheinfection.Theresearch,publishedin ProceedingsoftheNationalAcademyofSciences,wasinspiredby previouswork byotherresearchersshowingthat,bothintissuecultures(组织培养)andlive
4、mice,breastmilkfrom HIV-negativemotherswasnaturally endowedwith HIV-fightingproperties.Scientistssuggestedthatafewdifferentproteinsinthemilkcouldpotentiallyberesponsible,butnooneknewwhichone.Aspartofthestudy,theresearchersdividedbreastmilkintosmallerfractions(部分)madeupofspecificproteinsviaanumberoff
5、ilters(过滤)—separatingtheproteinsbysize,electricalchargeandother characteristics—andtestedwhichofthesefractions,whenaddedtoatissueculture,preventedthecellsfrombeinginfectedbyHIV.Eventually,they foundthatoneparticularproteinwaspresentinalltheHIV-resistantfractionsbutinnoneoftheothers:TenascinC.Tenasci
6、nCworksbyblockingakeyproteinon HIV’senvelope thatnormallytiesuptoareceptoronaTcell’smembranecalledCCR5.Indoingso,TenascinCpreventsHIVfrommixingwiththeTcellandinjectingitsRNAinside.Still,theresearcherssaythatothernaturalelementsinmilkmightplayaroleinfightingHIVaswell.“It’sclearlynotthewholestory,beca
7、usewedohavesamplesthathavelowamountsofthisproteinbutstillhaveHIV-neutralizingactivity,”thestudy’sleadauthorPermarsays. “Soitmaybeacting inconcertwith otherantiviralandantimicrobialfactorsinthemilk.”Wh
