Which of the Following Describes the Swahili Civilization's Relationship with the People

Which of the following describes the Swahili civilization's relationship with the people who lived in the interior?

A) Swahili kings expanded into the interior,eventually establishing an empire that stretched from coast to coast.
B) Swahili states demanded that people living in the interior pay an annual tribute to gain access to the coastal trade.
C) Swahili cities operated as intermediaries for people from the interior to sell their goods to Arab merchants.
D) Swahili culture spread throughout most of the interior,as evidenced by widespread acceptance of Islam.