Suppose That the Opportunity Costs of Production Differ Between Two

Suppose that the opportunity costs of production differ between two countries. We can conclude that:

A) it will not be possible for either country to gain from trading with the other.
B) if each country specializes and trades with the other, there will be an increase in the production of all commodities.
C) each country should produce some of all goods to promote self-sufficiency.
D) each country must have a comparative advantage of some goods.