Mrs. Smith helps me a lot my English. I often ask her help when I have problems with English.
A:to; for
B:with; for
C:with; about
D:for; with
已知a,b,c分别为△ABC三个内角A,B,C的对边,bcosC+3bsinC﹣a﹣c=0.求证:A,B,C成等差数列.