The people who migrated to melanesia developed
a. an advanced economy based on telecommunications and information technology.
b. protected settlements.
c. a culture based on art.
d. an economy based on trade.

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

The people who migrated to Melanesia developed an economy based on trade - d. 

An economy based on trade was one where the people who were involved were mostly trading among each other because this was the thing that they could do considering the fact that all of them were on one island.