In a Two-Way ANOVA, the Main Effect of a Factor

In a two-way ANOVA, the main effect of a factor is the

A) extent to which its effect depends on the action of the other factor.
B) extent to which the factor produces dependent variable scores different from those the other factor produced.
C) effect of changing the levels of the factor on the dependent variable scores, ignoring all other factors in the study.
D) effect of changing the levels of the factor on the dependent variable scores, taking into account all other factors in the study.