题目

已知a,b,c为△ABC的三个内角A,B,C的对边，向量m=(),n=(cosA,sinA),若mn,且acosB+bcosA=csinC,则角A,B的大小分别为(A)              (B)                  (C)             (D) 答案：C∵m⊥n,∴cosA-sinA=0.∴2sin(-A)=0.又∵A为△ABC内角,∴A=.∵acosB+bcosA=csinC,由正弦定理有sinAcosB+sinBcosA=sin2C,∴sin(A+B)=sin2C.∴sinC=sin2C.∴sinC=1.∴C=.∴B=.The island is__________attrative in spring and autumn because of the pleasant weather in both seasons. A．partly B．merely C．nearly D．equally