The guilds, banks, and money systems, which began in medieval europe,

The guilds , banks , and money system which began in medieval europe : Were the start of modern market economies and trade unions

Before the bank and money system, the merchants have to pay their goods with another goods in a barter system. This often create some dispute because of 'unfairness' . The money system allowed one specific currency as a standard to exchange goods and services and eliminate this unfairness

Your answer is b , public works