Which of the following is an example of a trade barrier?

A. Capitalism.
B. Tariff
C. Gross domestic product
D. Comparative advantage

B. Tariff

The correct answer is B. Tariff. Tariff is an example of a trade barrier. It is a tax or duty imposed on imported goods that makes them more expensive and less competitive compared to domestic products.

To determine which of the options is an example of a trade barrier, we need to understand what a trade barrier is.

A trade barrier refers to any government policy or regulation that restricts or hinders international trade. It is designed to protect domestic industries, businesses, and jobs by reducing foreign competition.

Now, let's evaluate each option:

A. Capitalism: Capitalism is an economic system and not a trade barrier. It is based on private ownership and the pursuit of profit through free exchange in markets.

B. Tariff: A tariff is a tax or duty imposed on imported goods and services. It makes foreign products more expensive, thereby providing protection to domestic industries by reducing competition from imports. Thus, a tariff is an example of a trade barrier.

C. Gross domestic product (GDP): GDP is a measure of the total value of goods and services produced within a country over a specific period. It is an indicator of an economy's size and strength but not a trade barrier.

D. Comparative advantage: Comparative advantage refers to a country's ability to produce a good or service at a lower opportunity cost than other countries. It is a concept that explains the benefits of free trade rather than being a trade barrier.

In conclusion, the correct answer is B. Tariff, as it represents a policy that imposes a tax on imported goods, thus acting as a trade barrier.