Using the Iso-Profit Line Solution Method to Solve a Maximization

Using the iso-profit line solution method to solve a maximization problem requires that we:

A) find the value of the objective function at the origin.
B) move the iso-profit line away from the origin until it barely touches some part of the feasible region.
C) move the iso-cost line to the lowest level that still touches some part of the feasible region.
D) test the objective function value of every corner point in the feasible region.
E) none of the above