Answer:
B. By controlling salt and gold trade routes
Step-by-step explanation:
The economic progression of Ghana from 750 to 1240 helped in the process of growth and territorial expansion by intensifying its trans-saharan trading activities in ivory, salt and gold. The development of huge urban complex also encouraged them in gaining monopoly over diffrent trading routes.
The Ghana Empire laid its dominance in Sahel region to the north of west African gold feilds. This enable Ghana to earn huge profit by the control of gold trade which turned region into wealthy and powerful.