Why was the battle of stalingrad seen as a turning point in the war?

What is true about the coins, shells, hides, and beads that have been used over time as currency? a.) they were usually found on island countries rather than in mainland-based countries. b.) they allowed the religious leaders to gain more wealth than their followers. c.) they were items of worth to the societies that used them. d.) they were always used by peasants rather than by the upper class.