It started in the Mongol Empire and spread via trade routes to all corners of Asia and the Middle East.
Explanation:
The roots of the plague are begun in central Asia, which around then was a piece of Mongol's domain. The Mongols regularly exchange with different realms in all sides of Asia and the Middle East.
The right answer is the third one: the bubonic plague originated in the Gobi Desert, part of the then Mongol Empire, around 1320. It then propagated to China and subsequently to India, Europe and Russia. The disease spread via trade routes mainly as a result of a poor hygiene. It never reached the American continent or Sub-Saharan Africa.
