Comparing the Fifty State-Level Economies in the United States with the Country-Level

Comparing the fifty state-level economies in the United States with the country-level economies in the Eurozone,  which of these statements best describes how close the two areas are to being an optimal currency area?

A) The Eurozone in general is closer to an optimal currency area than the fifty state economies in the United States.
B) The fifty state economies in the United States are more closely coordinated in their fiscal policies than the countries in the Eurozone and have a more flexible labor pool.
C) The use of the euro has been one step in making the Eurozone more integrated, even as the US states are moving away from being an optimal currency area.
D) The Eurozone is now considered to be as integrated as the fifty state-level economies in the United States.