The Quantity of Shoes Produced Is Measured Along the X-Axis

Multiple Choice

The quantity of shoes produced is measured along the x-axis of a bowed-outward production possibilities frontier and the quantity of shirts produced is measured along the y-axis. As you move down towards the right along the production possibilities frontier, the marginal cost of

A) a pair of shoes decreases.
B) a pair of shoes increases.
C) a shirt remains constant.
D) a shirt increases or decreases but we don't know for sure.
E) a pair of shoes and a shirt is equal at the midpoint between the x-axis and the y-axis.