In a two-factor experiment with 2 levels of factor A and 2 levels of factor B, three of the treatment means are essentially identical and one is substantially different from the others. What result(s) would be produced by this pattern of treatment means?

a) a main effect for factor A
b) a main effect for factor B
c) an interaction between A and B
d) The pattern would produce main effects for both A and B, and an interaction.