题目内容：
Questionsarebasedonthefollowingpassage.
EvenasAmericanshavebeengainingweight,theyhavecuttheiraveragefatintakefrom36to34percentoftheirtotaldietsinthepast15years．Andindeed,cuttingfattocontrolorloseweightmakessense.Fathasninecaloriespergram.Proteinandcarbohydrates(碳水化合物)havejustfour．Moreover,thebodyusesfewercaloriestometabolizefatthanitdoestometabolizeotherfoods．Comparedwithproteinandcarbohydrates--whichbreakdownintoaminoacidsandsimplesugars,respectively,andcanbeusedtostrengthenandenergizethebody--dietaryfatismoreeasilyconvertedtobodyfat．Therefore,it'smorelikelytostayonbuttocks,thighsandbellies.
Butcuttingfatfromyourdietdoesn'tnecessarilymeanyourbodywon'tstorefat．Forexample,betweennonfatandregularcookies,there'strivialdifferenceincaloriesbecausemanufacturersmakeupforthelossoffatbyaddingsugar．Low-fatcrackers,soupsanddressingscanalsobejustashighincaloriesasricherversions．Nomatterwherethecaloriescomefrom,overeatingwillstillcauseweightagain．Thecaloriesfromfatjustdoitalittlequicker．AWisconsincomputerprogrammerwhodecidedwithadietcoachtoeatonly40gramsoffatadaylearnedthelessonfirsthand．Hewasn'tlosingweight．Thenheshowedhisfooddiarytohiscoachandrevealedhe'dbeeneatinghalfapoundofjellybeansaday.
"Theydon'thaveanyfat,"heexplains．Buttheyhadenoughsugartokeephimfrom
sheddinganounce.
Nonfatfoodsbecomeadd-onfoods．Whenweaddthemtoourdiet,weactuallyincreasethenumberofcaloriesweeatperdayandgainweight．ThatwasborneoutinaPennsylvaniaStateUniversitystudy．Forbreakfast,Prof．BarbaraRollsgavetwogroupsofwomenyogurtthatcontainedexactlythesameamountofcalories．Onegroup'syogurtlabelsaid"highfat"--theother,"lowfat."The"lowfat"yogurtgroupatesignificantlymorecalorieslaterinthedaythantheothergroup．"Peoplethinkthey'vesavedfatandcanindulgethemselveslaterinthedaywithnoadverseconsequences,"saysRichardMattes,anutritionresearcheratPurdueUniversity．"Butwhentheydothat,theydon'tcompensateveryprecisely,andtheyoftenendupoverdoingit."
WhyareAmericansstillgainingweight? A．Theyeattoomuchfat.
B．Theyovereat.
C．Theyeatlow-fatcrackers,soupsanddressings.
D．Theyeatsugar.
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