Throughout most of African history, why did the main trade routes in sub-Saharan Africa run north and south?

A. Trading rules at the time required merchants to travel from north to south.
Trading rules at the time required merchants to travel from north to south.

B. The different climate zones changed from north to south across the continent; trade routes developed along common pathways
The different climate zones changed from north to south across the continent; trade routes developed along common pathways

C. Traders followed natural waterways, like rivers, which ran north to south.
Traders followed natural waterways, like rivers, which ran north to south.

D. Traders followed camel caravans that traveled north and south.