Refer to the Figure Shown, Which Represents the Production Possibilities

Refer to the figure shown, which represents the production possibilities frontiers for Countries A and B. The slope of Country A's production possibilities frontier:

A) measures the opportunity cost of trucks in terms of cars.
B) measures the trade-off that Country A faces when deciding how to allocate resources.
C) is constant, because the opportunity cost remains constant.
D) All of these statements are true.