If the United States and China decide to specialize and trade, which of the following must be true?

The correct answer highlights the importance of comparative advantage in international trade. When two nations specialize and trade, it is essential that they have different opportunity costs for producing goods. This difference in opportunity costs allows each country to produce the goods for which they have a comparative advantage, meaning they can produce a good at a lower opportunity cost than the other country.

If the U.S. and China have different opportunity costs, each can benefit from trading with the other. For example, if the U.S. can produce electronics more efficiently while China can produce textiles with less foregone value, they can both benefit by specializing in what they do best and trading for the other country's specialty.

In this context, options suggesting identical opportunity costs or identical production capabilities are incorrect; such situations would lead to no comparative advantage, and therefore, no incentive to trade. Focusing on inferior goods does not have an inherent connection to international trade specialization and could misrepresent the benefits that arise from trading based on comparative advantages. Thus, having different opportunity costs is fundamental for the benefits of trade to materialize.