Answer:
C. the establishment of the Yuan Dynasty :)
Explanation:
The Yuan Dynasty of China was established when Mongol nomads led by the notorious Genghis Khan and his grandson Kublai Khan eventually overran the Chinese army. The empire would grow to be the biggest contiguous land empire in history throughout its lifetime. After crushing the final Song opposition, Mongol emperor Kublai Khan officially instituted the Yuan dynasty in Chinese tradition in 1279, bringing China back together under Mongol sovereignty for the first time under the authority of a non-Han people.
I am 100% certain that's the answer :)
