Which of the following is a reason a country might put a tariff on imports?
a. to form an agency relationship
b. to increase its exports
c. to protect domestic companies
d. to create free trade

The reason why a country might want to put a tariff on its imports would be to protect domestic companies - c.

When a country creates tariffs on imports this means that they're charging extra the countries which want to import their things in the country. This effectively means they want to protect domestic companies.