Final answer:
Bantu-speaking peoples' innovations led to the foundation of the medieval kingdoms of Great Zimbabwe and Mapungubwe in southern Africa, mainly through their control of trade.
Step-by-step explanation:
The Bantu-speaking peoples brought innovations to southern Africa that were fundamental in the development of several prominent medieval kingdoms. The correct answer to the question about the innovations of Bantu-speaking peoples leading to the foundation of medieval kingdoms in southern Africa is c) Great Zimbabwe and Mapungubwe. These kingdoms flourished due to their control over local and regional trade, leveraging their strategic positions to network with the coastal civilization of the Swahili peoples. This allowed them to be interconnected with other parts of Africa and beyond, significantly contributing to their prosperity and expansion.