Comparative advantage. It is being able to produce goods by using fewer resources, at a lower opportunity cost, that gives countries a comparative advantage. The gradient of a PPF reflects the opportunity cost of production. Increasing the production of one good means that less of another can be produced.
The four river valley civilizations were the Tigris & Euphrates Valleys, the Nile River Valley, the Indus River Valley, and the Yellow River Valley. Civilizations developed around rivers because their waters provided places to hunt and fish. Also, as the rivers flooded, the lands around them became fertile.
You are suppoesed to choose a historic person during the rennasance times in the northern area. You need to research that person and learn about their impacts or their invention's impact on the world.
Yes, Ghana is in Africa. ;-)
