The kingdoms of ghana, mali, and songhai
prospered primarily due to their
(1) exchanges with indian ports
(2) direct access to the arabian sea
(3) control of trade routes
(4) abundance of diamonds

The kingdoms of Ghana, Mali, and Songhai prospered primarily due to their "(1) exchanges with Indian ports" but it should be noted there were other factors. 

Towns and small farms are usually for land, lakes, rivers, and seas.they also produce other food, like crops.it's also where animals are, where we get our meat.large plantations normally have forests, where crops are grown for sale. (similar to farms)plantations have larger fields of crops.our wine, sugar canes, and fruits come from plantations.