The Primary Economic Advantage of the European Union to Its

The primary economic advantage of the European Union to its members is that:

A) the tax structures of each participating nation have been made nearly identical
B) each nation is free to formulate its own trade policies
C) all participating nations use a common currency
D) the reduction of trade barriers permits producers to specialize based on the principle of comparative advantage
E) all labour and safety regulations are now standardized through the area