A Key Point in the Difference Between the United States

A key point in the difference between the United States and the European Union as OCAs, is that:

A) the intra-European Union trade is significantly higher than the intrastate trade in the United States.
B) the intra-European Union trade is significantly lower than the intrastate trade in the United States.
C) the intra-European Union labor migration is much higher than the intrastate migration in the United States.
D) in the United States, language creates a significant barrier.