Answer: A: The Sahara Desert
Explanation:"Salt from the Sahara desert was one of the major trade goods of ancient West Africa where very little naturally occurring deposits of the mineral could be found. Transported via camel caravans and by boat along such rivers as the Niger and Senegal, salt found its way to trading centres like Koumbi Saleh, Niani, and Timbuktu, where it was either passed further south or exchanged for other goods such as ivory, hides, copper, iron, and cereals. The most common exchange was salt for gold dust that came from the mines of southern West Africa. Indeed, salt was such a precious commodity that it was quite literally worth its weight in gold in some parts of West Africa."