The Two-Country PPF/indifference Curves Model Illustrates That

The two-country PPF/indifference curves model illustrates that:

A) whenever opportunity costs differ, specialization and trade can enhance national welfare.
B) differences in factor endowments and technology cause countries' production possibilities frontiers to differ, and these differences can explain comparative advantages.
C) differences in preferences can determine comparative advantage.
D) All of the above.
E) None of the above.