【初中英语完形一道小问题.Mr.Robinsonhadtotravelsomewhereonbusiness,andashewasinahurry,hedecidedtogobyair.Helikedsittingbesideawindowwhenhewasflying,sowhenhegotontotheplane,helookedforawindowseat.Hefound】

　　初中英语完形一道小问题.

　　Mr.Robinsonhadtotravelsomewhereonbusiness,andashewasinahurry,hedecidedtogobyair.Helikedsittingbesideawindowwhenhewasflying,sowhenhegotontotheplane,helookedforawindowseat.Hefoundallofthemhadalreadyhadbeentakenexceptforone.Therewasasoldiersittingintheseatbesidethisone,andMr.Robinsonwassurprisedthathehadnottakentheonebythewindow；but,anyhow,heatoncewenttowardsit.

　　Whenhereachedit,however,hesawthattherewasanoticeonit.Itwaswrittenininkandsaid,“Thisseatispreservedforproperloadbalance,thankyou.”MrRobinsonhadneverseensuchanunusualnoticeinaplanebefore,buthethoughtthattheplanemustbecarryingsomethingparticularlyheavyinit,sohewalkedonandfoundanotheremptyseat,notbesideawindow,【tositin.】

　　Twoorthreepeopletriedtositinthewindowseatbesidethesoldier,buttheytooreadthenoticeandwenton,whentheplanewasnearlyfull,averybeautifulgirlhurriedintotheplane.Thesoldier,whowaswatchingthepassengerscomingin,quicklytookthenoticeofftheseatbesidehimselfandinthiswaysucceededinhavingthecompanyofthegirlduringthewholetrip.

　　我想问的是在我画的那个【tositin】前如果不加逗号,那么是应该用以下哪一个?

　　AtositBtobesatCtositonDtobesaton