Answer: d. Mongols
Explanation:
Under Genghis Khan and his descendants, the Mongols developed the largest land empire that the world has ever seen with their dominions stretching from the pacific coast of Asia to Eastern Europe.
In their lands, they reestablished the Silk Road and offered such protection on it that trade flourished in the empire and even continued after the empire shrank. They also developed a tribute system to ensure the empire remained rich.
