There is an opportunity cost for all economic choices because:

The opportunity cost of a choice is the value of the best alternative given up. Scarcity is the condition of not being able to have all of the goods and services one wants. It exists because human wants for goods and services exceed the number of goods and services that can be produced using all available resources.

Explanation:

(a).national trade check first good luck

trade regulation is a field of law, often bracketed with antitrust (as in the phrase “antitrust and trade regulation law”), including government regulation of unfair methods of competition and unfair or deceptive business acts or practices. antitrust law is often considered a subset of trade regulation law. franchise and distribution law, consumer protection law, and advertising law are sometimes considered parts of trade regulation law.

in general the theory of economics says that the more open to trade a country is the better   the result for the same country and the whole economies.

in real life countries impose taxes, quotas, etc which is not so good for the economies.

this kind of commercial war between the usa and china is slowing down the growth of the whole world so we can say that it is a draw back of trade regulations. and the free trade agreements are benefits of trade regulations.