题目内容：
[1]Stampcollectorsusuallycollectstampsonlyfromcertaincountriesorregions.Thetraditionalmethodofstampcollectingistoorganizestampcollectionaccordingtotheissuedates.[2]Ofcourse,therearemany____________.Youcancollectstampsrelatingtoaparticulartheme.Forexample,sportloversmaychoosetheOlympictheme.TheytrytheirbesttofindOlympicstampsissuedbyvariouspartsoftheworldeveryfouryears.Someofthemmaywanttoconcentrateonevenmorespecificsportactivitieslikeballgames,gymnasium,swimming,etc.
[3]Ifyoulikeastronomy,youmaybekeenoncollectingstampsdescribingthestars,planets,spacecraft,spacemen,etc.onceyouhavefixedthetopic,younolongerneedtobotheraboutstampsotherthanthethemeyouselected.Then,youcanputallyourefforttocollectthestampsaroundit.
[4]Chinaissueszodiacanimalstamps(十二生肖邮票)everyyeartocelebratetheLunarNewYear.Theyareextremelypopularandalotofcollectorswaitpatientlyfor12yearstocollectafullsetofthem.HongKong’sLunarNewYearspecialstampseriesbeganin2000withtheYearofDragonandthetwelfthandfinalsetwasissuedin2011,theYearofRabbit.RecentlysomeWesterncountrieshaveissuedzodiacanimalstamps,whichattractalotofattentionaswell.
[5]Youmaychooseanythemeyoulike.However,youshouldbearinmindanessentialpoint.Thetopicyouchooseshouldnotbetoonarrow.Otherwise,itisverydifficulttoaccumulatestampsaroundthetopic.Youwillbedepressedandevenloseyourinterestincollectingstamps.
[6]Collectingstampswiththeseisespeciallypopularamongteenagersbecausethereisawiderangeofchoicesforthem.Themainchallengeishowyouorganizeandexpandyourcollectionaroundyourtheme.
Whatisthemainideaofthepassage?（nomorethan5words）
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