Correct answer choice is :
4) Cultural diffusion between different societies
Step-by-step explanation:
Ancient trade crossed the northeastern edge of the Sahara in the Naqadan period. Predynastic Egyptians in the Naqada I period traded with Nubia to the south, the oases of the Western Desert to the west, and the customs of the eastern Mediterranean to the east. Many exchanging tracks went from oasis to oasis to resupply on both food and water. These refugees were very significant. They also shipped obsidian from Ethiopia to form swords and other things.