依题意,可求得(sinA-sinC)2=0,从而可利用正弦定理求得a=b=c,继而可得答案.
【解析】
∵△ABC中,sinB既是sinA,sinC的等差中项,又是sinA,sinC的等比中项,
∴2sinB=sinA+sinC,sin2B=sinA•sinC
∴4sin2B=(sinA+sinC)2
∴4sinA•sinC=(sinA+sinC)2
(sinA+sinC)2-4sinA•sinC=0
即(sinA-sinC)2=0,
∴sinA=sinC,
于是2sinB=2sinA=2sinC,
∴sinB=sinA=sinC,
即:a=b=c,
∴B=60°
故选C.