B is correct. A comparative advantage arises if one entity can produce an item at a lower opportunity cost than another. An absolute advantage in producing a good (or service) arises if one entity can produce that good at a lower cost or use fewer resources in its production than its trading partner. Even if a country does not have an absolute advantage in producing any of its goods, it can still gain from trade by exporting the goods in which it has a comparative advantage. The country with the lower opportunity cost (with the comparative advantage) should specialize and produce its low opportunity cost item, and the other country should produce the high opportunity cost item, trading the goods between each other to make both better off.