Answer:
B. The PPF is a straight line because of the opportunity cost of the two goods is constant.
Explanation:
The graphic representation of the PPF is a downward line with slope -1. The trade-off is always the same, the trade-off is always 1, in the problem statement when the economy produces 10 more of the Y product, the economy stops producing 10 of product X. The cost of opportunity of the good X is always 1 of the Y.