Answer:
Option: D. A complex network of internal waterways that provided cheap transportation.
Explanation:
Both Tang and Song dynasties were economically strong and much more flourished in farming and trade. The economy was very prosperous in both dynasties. The rise of the economy in the dynasties came when they allowed cheap transportation in China by waterway. The waterway became the main route for transporting the goods and led in the rise of the oversea trade.