Comparative Advantage: To determine comparative advantage, we need to calculate the opportunity cost of producing one unit of each good in terms of the other. For Spain, the opportunity cost of producing 1 litre of wine is 1 kilo of cheese (2 kilos of cheese / 2 litres of wine). For Portugal, the opportunity cost of producing 1 litre of wine is 3 kilos of cheese (12 kilos of cheese / 4 litres of wine). Therefore, Portugal has a comparative advantage in wine, as it has a lower opportunity cost of producing wine compared to Spain. Since each country has a comparative advantage in one good, the answer is