The Following Data Show the Means for Four Treatment Conditions

The following data show the means for four treatment conditions as well as the overall means for the columns and the rows. For these data, what numbers are compared to assess the main effect of factor A? $$\begin{array} {| l | l | l | l| } \hline \mathrm { B } 1 & \mathrm { M } = 20 & \mathrm { M } = 60 & \mathrm { M } = 40 \\\mathrm { B } 2 & \mathrm { M } = 30 & \mathrm { M } = 70 & \mathrm { M } = 50\\\hline\end{array}$$

A) 30; 70
B) 20; 30
C) 40; 50
D) 25; 65