All of the Following Are Examples of Factors That Affect

All of the following are examples of factors that affect trading activity between countries except __________________.

A) Charging a 0.75% import tax on steel imported from China into the U.S.
B) Charging $3 tariff per barrel of crude oil imported in the U.S.
C) Restricting the importation of produce into the U.S from South America
D) All of these are factors that affect trading activity between countries