B. He conquered the last of the Song Dynasty and brought China under Mongol rule.
Explanation:
Kublai Khan is one of the best known Mongol rulers, both for good and for bad. He was the grandson of Genghis Khan, and unlike his grandfather and father, he ruled in a manner that promoted tolerance among the different groups of people. One of the things by which Kublai Khan is best known is that he was the first Mongol to conquer and rule all of China.
Kublai Khan managed to conquer the last independent Chinese state, the Song Dynasty, incorporated it into the Mongol Empire, and formed the Yuan Dynasty. While this was seen as a great success and promised a long lasting and powerful empire, Kublai Khan also made some mistakes (mostly military ones) that actually started off the decline of the empire.
