$\begin{array}{1 1}\text{Plot of }p_A\text{ versus }x_A\text{ (mole fraction of A in liquid phase) is linear}\\\text{Plot of }p_B\text{ versus }x_B\text{ is linear}\\\text{Plot of }p_{total}\text{ versus }x_A\;(or\; x_B)\text{ is linear}\\\text{Plot of }p_{total}\text{ versus }x_A\text{ is nonlinear}\end{array} $