Why was the city of Timbuktu significant in the 14th century?

Historically, the City of Timbuktu was popular as a trading station on the trans-Saharan (caravan) route. ... By the 14th century, it was a thriving centre for gold and salt trade. Some of the oldest mosques built during the 14th century included Sankore, Sidi Yahia, and Djinguereber.

a widespread disease that killed many people

the split of the christian church

invasion from arab muslims

i think the answer is   b.