Which was one of the mongol empires major economic accomplishments

Which of the following describes one of the Mongol Empire's major economic accomplishments?

A. The Mongol Empire was the first large state to introduce paper money.
B. The Mongol Empire plundered the territories it captured, devastating the economies of entire regions.
C. The Mongol Empire was led by rural farmers and converted its conquered territory to farmland.
D. The Mongol Empire guarded roads carefully to promote trade throughout its territory.

The answer is D.