Answer :
Imposing some sort of cost on trade that raises the price of the traded products is most likely an example of a "trade barrier" because it discourages the trading of that product.
I believe the answer is: A.a trade barrier
Trade barrier refers to the regulation made by a country to limit the amount of goods that could be imported from another country.
The purpose of a trade barrier is to rise the imported product so the local products could thrive and win the competition in local market.