题目内容：
Questionsarebasedonthefollowingpassage. Exerciseisoneofthefewfactorswithapositiveroleinlong-termmaintenanceofbodyweight.Unfortunately,thatmessagehasnotgottenthroughtotheaverageAmerican,whowouldrathertryswitchingto“light”beerandlow-caloriebreadthanincreasephysicalexertion.TheCentersforDiseaseControl,forexample,foundthatfewerthanone-fourthofoverweightadultswhoweretryingtoshedpoundssaidtheywerecombiningexercisewiththeirdiet.
Inrejectingexercise,somepeoplemaybediscouragedtoomuchbycaloric-expenditurecharts:forexample,onewouldhavetobrisklywalkthreemilesjusttoworkoffthe275caloriesinonedeliciousDanishpastry（小甜饼）.Evenexerciseprofessionalsconcedehalfapointhere.“Exercisebyitselfisaverytoughwaytoloseweight,”saysYorkOnnen,programdirectorofthePresident’sCouncilonPhysicalFitnessandSports.
Still,exercise’ssupportingroleinweightreductionisvital.AstudyattheBostonUniversityMedicalCenterofoverweightpoliceofficersandotherpublicemployeesconfirmedthatthosewhodietedwithoutexerciseregainedalmostalltheiroldweight,whilethosewhoworkedexerciseintotheirdailyroutinemaintainedtheirnewweight.
Ifyouhavebeensedentary（极少活动的）anddecidetostartwalkingonemileaday,theaddedexercisecouldburnanextra100caloriesdaily.Inayear’stime,assumingnoincreaseinfoodintake,youcouldlosetenpounds.Byincreasingthedistanceofyourwalksgraduallyandmakingotherdietaryadjustments,youmayloseevenmoreweight.
WhatissaidabouttheaverageAmericaninthe&nb
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