To What Extent Did Islam Successfully Penetrate the Populations of East

To what extent did Islam successfully penetrate the populations of east Africa?

A) As in Asia the conversion of the coastal cities led to almost complete conversion of the populations lying inland.
B) Most of the clans and the most important lineage groups outside of the east African cities were converted to Islam in order to participate in trade.
C) Islam penetrated very little into the interior among the hunters, pastoralists, and farmers, and even the areas near the trading towns remained relatively unaffected.
D) Islam spread from the cities to the hinterland in such a way that eventually the countryside was more Islamic than were the cities.