题目内容：
根据以下材料，回答题
EatingChocolate
Goodnewsforchocoholics:thetreatpreferredbymillionsallovertheworldisgoodforyou,accordingtoAmericanresearchersattheUniversityofCalifornia．Chocolatecontainssubstancescalledflavonoidsthatcanhelpmaintainahealthyheartandgoodcirculation．Theresearchershavediscoveredthatcocoaactslikeaspirinandthateatingabarofchocolatehasalsobeenshowntoreleaseendorphinsinthebody:thesechemicalshelptoreducepainandstressandmakeyoufeelhappy.
TheOlmecIndiansofMexicoandCentralAmericawerethefirsttogrowcocoabeans,inabout1500B.C.,andtheMayasweredrinkingunsweetenedcocoahundredsofyearsbeforeitbecamefashionableinEurope.
In1544,adelegationofMayannoblesvisitedPhilipofSpainandgavehimjarsofcocoaasagift．CocoasoonbecamefashionableinSpainandPortugal．TheSpanishwerethefirsttoaddsugartotheircocoadrink.
Bythemiddleofthecentury,solidchocolatewasbecomingfamiliar．In1765,JamesBakerandJohnHananopenedthefirstchocolatemillintheUnitedStates,introducingchocolatetotheaveragecitizen．In1896,inSwitzerland,DanielPeterhadtheideaofaddingmilkinthechocolate-makingprocessandproducedthefirstmilkchocolate.
Sincethen,chocolatehasgrownenormouslyinpopularity．Oneofthebiggestchocolate-eatingnationsisBritainwheretheaverageman,woman,andchildeatsninekilosofchocolateayear．Infact,chocolateisthenumberonecomfortfoodandtherearemorechocoholicsinBritainthanany-whereelseintheworld．Researcherswarnthatalthoughchocolateisgoodforyou,itshouldbeeateninsmallquantitiesandwithnoaddedmilk.
Whyischocolategoodforheartsandcirculation? A．Itreducespainandstress．
B．Itcontainssubstancescalledflavonoids.
C．Itreleasesendorphinsinhumanbody．
D．Itactslikeaspirintoprotecthearts.
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