题目内容：
根据下列短文，回答题：(B)Youmaythinkthatsailingisadifficultsport,butitisreallynothardtolearnit.Youdonotneedtobestrong.Butyouneedtobequick.Andyouneedtounderstandafewbasicrulesaboutthewind.
First,youmustaskyourself,“Whereisthewindcomingfrom?Isitcomingfromaheadorbehindorfromtheside?”Youmustthinkaboutthisallthetimeontheboat.Thewinddirectiontellsyouwhattodowiththesail.
Let’sstartwiththewindblowingfromthebehind.Thismeansthewindandtheboataregoinginthesamedirection.Thenyoumustalwayskeepthesailoutsidetheboat.Itshouldbeata90°angle(角度)totheboat.Thenitwillcatchthewindbest.
Ifthewindisblowingfromtheside,itisblowingacrosstheboat.Inthiscase,youmustkeepthesailhalfwayoutsidetheboat.Itshouldbeata45°angletotheboat.Itneedstobeoutfarenoughtocatchthewind,butitshouldn’tflap(摆动).Itshouldn’tlooklikeonaflagpole.Ifitisflapping,itisprobablyouttoofar,andtheboatwillslowdown.
Sailingintothewindisnotpossible.Ifyoutry,thesailwillflapandtheboatwillstop.Youmaywanttogointhatdirection.Itispossible,butyoucan’tgoinastraightline.Youmustgofirstinonedirectionandtheninanother.Thisiscalledtacking.Whenyouaretacking,youmustalwayskeepthesailinsidetheboat.
Whatshouldyouconsiderfirstwhilesailing? A．Sailors’strengt
B．Wavelevel
C．Winddirection
D．Sizeofsail
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