GMAT Critical Reasoning (CR) | Re: Historically, monetary systems

Historically, monetary systems have developed only in population centers with marketplaces. Through the fourth century B.C., Mesopotamian cities engaged in trade, but had never had marketplaces. By that period, however, Greek cities all had marketplaces, or agorae. The Greek cities’ agorae were centrally located and goods were traded there either for money or for commodities.

If all of the statements in the passage are true, then which one of the following must also be true?

(A) In the fourth