It is absolutely ethical to charge those with lower incomes less money, and those with higher incomes more money.
Encouraging free trade between countries and helping countries negotiate trade conflicts are two most important jobs of the World Trade Organization. Most countries in the world are members of the said organization.
The answer would be letter D. World Trade Organization.
People were able to specialize and trade, which made their city wealthier, stronger, and even more likely to make allies. :)
