In a two-way between subjects ANOVA, a significant main effect for B means that

A - the mean for B1 is not equal to the mean for B2.

B - the difference between A1 and A2 is not the same at B1 as for B2.

C - the mean for A1 is equal to the mean for A2.

D - the mean for B1 is equal to the mean for B2.