How Did the Expansion of Islam Aid in the Creation

How did the expansion of Islam aid in the creation of international trade on the east African coastline?

A) Islam expanded to India and southeast Asia providing a religious bond of trust between those regions and the converted rulers of the cities of east Africa.
B) Because Islam regarded Christians as peoples of the book, Muslim merchants came to trade at the Christianized ports of east Africa.
C) The connection with the Islamic states of north Africa permitted the urbanized ports of east Africa to trade widely with northern Europe.
D) The direct trade routes between the African states of west Africa and the coast of east Africa stimulated commerce between the cities of the east and the Atlantic Ocean.