When the Level of Capital Is Plotted on the Vertical $\mathrm { W }$

Multiple Choice

When the level of capital is plotted on the vertical axis and the level of labor is plotted on the horizontal axis, the slope of the isocost line is (assuming $\mathrm { W }$ is the price of labor and $r$ is the price of capital and production uses only these two inputs) :

A) $- w / r$
B) $- r / w$
C) $M P _ { K } / 1 P _ { 1 }$
D) $M _ { 1 } / M P _ { K }$