In what way was Kublai Khan more successful than Genghis Khan?

A. Kublai Khan was able to spread Daoism throughout Asia, while
Genghis Khan was not.
B. Kublai Khan was able to conquer all of China, while Genghis Khan
was not.
C. Kublai Khan was able to unify the Mongols, while Genghis Khan
was not
D. Kublai Khan was able to establish a civil service exam system,
while Genghis Khan was not.