If Pizza Is Measured on the Horizontal Axis and Pretzels

If pizza is measured on the horizontal axis and pretzels are measured on the vertical axis,the slope of the production possibility frontier at a given combination reflects

A) the total cost of producing that combination.
B) the total cost of producing that quantity of pizza in terms of pretzels.
C) the cost of making the last pizza in terms of pretzels.
D) the cost of making the last pretzel in terms of pizza.