The correct answer is B) As trade expanded to cover greater distances, a unit of exchange became more important.
A money economy began to replace the barter economy in the High Middle Ages and trade expanded to cover greater distances, a unit of exchange became more important.
In the economy of the Middle Ages, money represented the way to trade based on similar values for goods that beforehand, were bartered according to necessities.
As trade expanded to cover greater distances, the unite of exchange became the more precise way to exchange for goods, animals, minerals, vegetables, and other products. It was easier to handle for both parties that agreed on the value of things.
The other options of the question were a) as wars halted trade, merchants found new work metalsmithing or creating coins, c) Eastern merchants banded together to reject the barter economy in Europe, and d) Western merchants were no longer willing to negotiate trade agreements with Eastern nations.