By the mid 600s, Islam had begun to spread into northern Africa through Arabs who traveled across the Red Sea. From there, African religious leaders began to spread Islam throughout the eastern coastal regions of Africa. Over time, it further spread west across the continent, reaching the Ghana empire.

Based on the information in the passage, Islam was able to spread across Africa through
A.
the Crusades.
B.
the Silk Road.
C.
Muslim conquest.
D.
trans-Saharan trade.