Which of the Following Statements Is True

Which of the following statements is true?

A) When a nation has an absolute advantage over other nations in producing all goods and services, it cannot gain from trade.
B) Absolute advantage relates to production per unit of inputs, and comparative advantage involves the opportunity cost of producing different goods.
C) When a nation has an absolute disadvantage over other nations in producing a good, it cannot gain from trade.
D) Absolute advantage involves the opportunity cost of producing different goods, and comparative advantage relates to production per unit of inputs.