The correct option is:
A. Their geographic locations
Both the Axum Empire and the Swahili city-states thrived as trade empires primarily due to their strategic geographic locations. The Axum Empire was situated near major trade routes connecting Africa, the Arabian Peninsula, and the Mediterranean, while the Swahili city-states were located along the east African coast, facilitating trade across the Indian Ocean with merchants from the Middle East, India, and beyond. This advantageous positioning allowed them to control and benefit from trade networks.