题目内容：
回答题：Late-NightDrinking Coffeeloversbeware．Havingaquick"pick-me-up"cupofcoffeelateinthedaywillinterruptyoursleep．Aswellasbeingastimulant,caffeineinterruptstheflowofmelatonin,thebrainhormonethatsendspeopleintoasleep.
Melatoninlevelsnormallystarttoriseabouttwohoursbeforebedtime．Levelsthenpeakbetween2amand4am,beforefallingagain．"It'stheneurohormonethatcontrolsoursleepandtellsourbodywhentosleepandwhentowake,"saysMauriceOhayonoftheStanfordSleepEpidemiologyResearchCenteratStanfordUniversityinCaliforniA．ButresearchersinIsraelhavefoundthatcaffeinatedcoffeehalvesthebody'slevelsofthissleephormone.
LotanShiloandateamattheSapirMedicalCenterinTelAvivUniversityfoundthatsixvolunteerssleptlesswellafteracupofcaffeinatedcoffeethanafterdrinkingthesameamountofdecal．Onaverage,subjectsslept336minutespernightafterdrinkingcaffeinatedcoffee,comparedwith415minutesafterdecal．Theyalsotookhalfanhourtodropoff,twiceaslongasusual.
Inthesecondphaseoftheexperiment,theresearcherswokethevolunteerseverythreehoursandaskedthemtogiveaurinesample.Shilomeasuredconcentrationsofabreakdownproductofmelatonin．Theresultssuggestthatmelatoninconcentrationsincaffeinedrinkerswerehalfthoseindecaldrinkers.InapaperacceptedforpublicationinSleepMedicine,theresearcherssuggestthatcaffeineblocksproductionoftheenzymethatdrivesmelatoninproduction.
Becauseitcantakemanyhourstoeliminatecaffeinefromthebody,Ohayonrecommendsthatcoffeeloversswitchtodecafafterlunch.
Theauthormentions"pick-me-up"toindicatethat A．melatoninlevelsneedtoberaised
B．coffeeisastimulant
C．neurohormonecanwakeusup
D．caffeinecanbalanceourbrainhormone
参考答案：
答案解析：