What are two ways the European Union and the euro changed the way European countries interact with each other?

What would lead a historian to consider two events to have a relationship of correlation rather than causation

Which of the following inventions most directly allowed ancient farmers to produce a surplus ?

Who ever answers first gets ! trade in the vedic age led to a.the rise of kingdoms because of the importance of controlling land and long-distance travel routes b.the building of an extensive system of roads because of the difficult terrain c.the creation of a large banking class because of the need to exchange different currencies d.the development of a centralized government that controlled the economic decisions of its people