The principle that "trade can make everyone better off" applies to interactions and trade between A. families. B. states within the United States. C. nations.

The correct answers are all of the above options

Explanation:

Trade is the term which is defined as the activity of exchanging, buying or selling the goods and the services among the countries, people, families, nations.

It offers the variety or range of the products which could be sold in the market in order to earn or gain profit so that could benefit the business or themselves.

So, it could be better off when applies to the trade and interactions among the families, nations and states within US.