How did the Kingdom of Ghana facilitate the gold trade despite not having gold mines?

A. It established tax-free trade routes outside its borders to attract more traders to the gold mines.
B. It made it mandatory for all its buildings to be made of gold, thereby earning the name "Land of Gold."
C. It forced its traders to bring back gold from foreign gold mines and exchange it for salt.
D. It regulated the trade of gold by taxing merchants who used trade routes that passed through Ghana.