题目内容：
Mr.Joneswokeearlyonemorning，beforethesunhadrisen.Itwasabeautifulmorning，_31_hewenttothewindowandlookedout.Hewas_32_toseeaneatly-dressedandmid-agedprofessor，who_33_intheuniversityjustuptheroadfromMr.Jones‘house，comingthedirectionofthetown.Hehadgreyhairthickglasses，andwas_34anumbrella，amorningnewspaperandabag.Mr.Jonesthoughtthathemusthave_35_bythenighttrain_36_takingataxi.Mr.Joneshadabigtreeinhisgarden，andthechildrenhadtiedalong_37_tooneofthebranches，sothattheycouldswingonit.
Mr.Jonessawtheprofessor_38_whenhesawtheropeandlookedcarefullyupanddowntheroad.Whenhesawthattherewas_39_insight，hesteppedintothegarden(therewasnofence)，puthisumbrella，newspaper，bagandhatnearlyonthegrassand_40_therope.Hepulledit_41_toseewhetheritwasstrongenoughtotakehisweight，thenranasfastashecouldandswungintothe_42_ontheendoftherope，hisgreyhairblowingallaround_43_._44_heswung，sometimestakingafewmore_45_stepsonthegrasswhentheropebegantoswing_46_slowlyforhim.
_47_theprofessorstopped，straightenedhistie，combedhishaircarefully，putonhishat，_48_hisumbrella，newspaperandbag，andcontinued_49_hiswaytotheuniversity，lookingas_50_andcorrectandrespectableasonewouldexpectaprofessortobe.
_________
A.because
B.as
C.so
D.for
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