Answer: D. construction and protection of roads that ensured safe and easy travel
Step-by-step explanation:
Under Genghis Khan and his descendants, the Mongols conquered much of Asia and some of Eastern Europe such that they created the largest land empire ever seen.
Even though these Mongols could be brutal in conquest, they increased trade in the region by repairing the networks of roads that connected their conquered areas as well as constructing more. The protection they afforded these roads was renowned thus making travel easy.