The correct answers to this question are "rice" and "agriculture."
Although West Africa was rich in natural resources, it experienced political instability when different tribes and kingdoms vied for control over the rice trade. This political turmoil was one of the factors that caused agriculture to grow in Africa.
West Africa countries are blessed for the number of raw materials and natural resources it has. This was known by the European powers that needed so much those raw materials for their industries. That is why their expansionist plans included this part of Africa. West Africa countries traded cotton, gold, metal ornaments. What these countries imported was copper, salt, and horses.