The correct answer is Swahili.
Swahili developed as a result of trade interactions between various city-states along the East African coast, particularly those involved in trade with Arab merchants. It is a Bantu language that incorporated many Arabic words and elements due to these interactions, which were crucial for facilitating trade in the region.
Greek, Arabic, and Latin do not fit this context as they do not specifically arise from the trading dynamics of East African city-states.