The answer is D. an Economy based on trade
Unlike us who used money as a trading tools, those people back then use to trade a property they own if they want to acquire something.
If we want to acquire a product, lets say we want a dozen of eggs. We simply just gave a store owner $ 3 and we will get it. If those Melanesian wanted a dozen of eggs, they probably have to trade it with a Gallon of milk for example.
This kind of Economy also known as Barter Economy