题目内容：
Ihandbeensittingbymyselfinmyusualcompartmentforatleasttenminutes，waiting__31__.ThetrainsfromLittleburyneverseemedtostart__32__andIoftenthoughtthatIcouldhave__33__inbedalittlelongerorhad__34__cupofteabefore__35__.SuddenlyIheardsomeoneshouting__36__theplatformoutside.Ayounggirlwasrunningtowardsthetrain.Theman__37__putouthishandtostopherbutsheranpasthimandopenedthedoorofmycompartment.Thenthewhistleblewandthetrainstarted.
“Inearlymissedit，__38__?”thegirlsaid.“Howlongdoesittaketo__39_London?”“Itdependsonthe__40__.”Isaid.“Somedaysit‘s__41__others.”“I‘llhavetohavemywatchmended，__42__lateagaintomorrow，”shesaid.“It’smyfirstday__43__withanewfirmtodayandtheytoldmethattheman__44__isverystrict.I__45__himyetsoIdon‘tknow__46__buthesoundsabitfrightening.”Shetalkedabouthernewjob__47__thewaytoLondonandbeforelong，Irealizedthatshewasgoingtoworkformyfirm.My__48__secretaryhadjustleftsoImustbehernewboss.__49__onlyfairtotellher.“Oh，dear，”shesaid.“__50__mistake!IwishIhadknown.”“Nevermind，”Isaid.“Atleastyou‘llknowwhenyourtrain’slatethatminewillbe，too.”__________
A.thetraintostart
B.forthetrainstart
C.thetrain‘sstart
D.forthetraintostart
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答案解析：