Which of the following statements is true about comparative advantage? O.a) Comparative advantage is interesting theoretically, but it is not relevant when evaluating real-world economic conditions....

Which of the following statements is true about comparative advantage?

O.a) Comparative advantage is interesting theoretically, but it is not relevant when evaluating real-world economic conditions.
O.b) Comparative advantage exists whenever one person, firm, or nation can do something at lower opportunity costs than some other individual, firm, or nation.
O.c) Comparative advantage exists whenever one person, firm, or nation can do something at higher opportunity costs than some other individual, firm, or nation.
O.d) Only technologically advanced economies can have a comparative advantage in the production of a good or service.