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 One of the reasons why Country A and Country B are not realistic representations of actual countries is:

A) the production possibilities curves are straight lines; realistic ones would be concave.
B) they only represent the production of two goods.
C) they only represent two countries.
D) All of these statements are true.